The Reichsbürger claims are not really true, but they are also not completely baseless.
Germany is not a fully sovereign state, it has a de-facto constitution but refuses to call it officially "constitution": it is not Verfassung der Bundesrepublik (constitution of the Federal Republic) but it is still called Grundgesetz der Bundesrepublik (Basic Law of the Federal Republic) and historically the Grundgesetz was indeed officially not a constitution, but a ersatz constitution or interim constitution.1
There is no real peace treaty, only a treaty serving as a historical, de-facto one. Technically there never was German re-unification, only the "accession of 5 new federal states into the territory were the Grundgesetz is in force".
Many valid legal interpretations might successfully argue that the two points from the claims are technically true to varying extents, although in reality and in the de-facto situation, they are all not true.
Does Germany have a peace treaty and a constitution?
They have nothing called a peace treaty but a treaty that functions as one. They have nothing called a constitution, but declared that the Basic Law that explicitly never was a real constitution now is a real constitution.
The sad thing is, these Reichsbürger are usually completely crazy or just criminal people, with some of the most prominent proponents more comparable to the Emperor of America, despite most of them just a tiny bit to the right from mainstream conservatives in Germany today.
But in these two specific points from the claim in question they have some valid arguments in their hand, in theory at least. It is quite complicated because of the trickery involved in the historical events – always initiated by the German government – as they unfolded and as they and there consequences are now, or have to be, interpreted.
The case for "no real constitution"
These arguments are historically grown. When West-Germany was founded, it did not have sovereignty and no "real" constitution. Both points resulting from allied control over the German lands and emerging states. The West-German state held the view that it was the only legitimate German state and successor to the German Reich, giving itself a preliminary constitution, called Grundgesetz (Basic Law), until all German lands are again unified, including the GDR and crucially, all other territories in the East, now in Poland and Russia, that were internationally accepted parts of the Reich before 1937.
Grundgesetz, Fassung 23. Mai 1949:
Im Bewußtsein seiner Verantwortung vor Gott und den Menschen, von dem Willen beseelt, seine nationale Einheit zu wahren und als gleichberechtigtes Glied in einem vereinten Europa dem Frieden der Welt zu dienen, hat sich das Deutsche Volk in den Ländern Baden, Bayern, Bremen, Hamburg, Hessen, Niedersachsen, Nordrhein-Westfalen, Rheinland-Pfalz, Schleswig-Holstein, Württemberg-Baden- und Württemberg-Hohenzollern, um dem staatlichen Leben für eine Übergangszeit eine neue Ordnung zu geben, kraft seiner verfassungsgebenden Gewalt dieses Grundgesetz der Bundesrepublik Deutschland beschlossen.
Es hat auch für jene Deutschen gehandelt, deren mitzuwirken versagt war.
Das gesamte Deutsche Volk bleibt aufgefordert, in freier Selbstbestimmung die Einheit und Freiheit Deutschlands zu vollenden.
Translation: (Basic Law, version from May, 23rd 1949)
Aware of his responsibility before God and mankind, the German people in the states of Baden, Bavaria, Bremen, Hamburg, Hesse, Lower Saxony, North Rhine-Westphalia, Rhineland-Palatinate, Schleswig-Holstein, Württemberg-Baden- and Württemberg-Hohenzollern, have been inspired by the will to preserve their national unity and to serve the peace of the world as an equal member in a united Europe, in order to give state life a new order for a transitional period, adopted this Basic Law of the Federal Republic of Germany by virtue of its constitutional power.
It has also acted for those Germans who were unable to participate.
The entire German people are called upon to complete Germany's unity and freedom in free self-determination.
This provisional Grundgesetz left Germany(West) under ultimate allied (West) control.
Wikipedia: Basic Law for the Federal Republic of Germany
The German word Grundgesetz may be translated as either Basic Law or Fundamental Law (Grund- is cognate with the English word ground). The term Verfassung (constitution) was deliberately avoided as the drafters regarded the Grundgesetz as an interim arrangement for a provisional West German state, expecting that an eventual reunified Germany would adopt a proper constitution, enacted under the provisions of Article 146 of the Basic Law, which stipulates that such a constitution must be "freely adopted by the German people". Nevertheless, although the amended Basic Law would finally be approved in 1990 by all four Allied Powers (who thereby relinquished their continued reserved constitutional rights), it was never submitted to a popular vote, neither in 1949 nor in 1990.
The Grundgesetz was constructed given the West-Germans two different ways to re-expand eastwards. Any little irridenta tribe and small conglomeration might declare its accession into the Grundgesetz territory – or the "whole German people are reunited after the peace", when crucially the German people were called to give themselves a real constitution.
Artikel 23 GG:
Dieses Grundgesetz gilt zunächst im Gebiete der Länder Baden, Bayern, Bremen, Groß-Berlin, Hamburg, Hessen, Niedersachsen, Nordrhein-Westfalen, Rheinland-Pfalz, Schleswig-Holstein, Württemberg-Baden und Württemberg-Hohenzollern. In anderen Teilen Deutschlands ist es nach deren Beitritt in Kraft zu setzen.
This Basic Law initially applies in the states of Baden, Bavaria, Bremen, Greater Berlin, Hamburg, Hesse, Lower Saxony, North Rhine-Westphalia, Rhineland-Palatinate, Schleswig-Holstein, Württemberg-Baden and Württemberg-Hohenzollern. In other parts of Germany, it shall enter into force after their accession.
But compare that to:
Artikel 146 GG, original:
Dieses Grundgesetz verliert seine Gültigkeit an dem Tage, an dem eine Verfassung in Kraft tritt, die von dem deutschen Volke in freier Entscheidung beschlossen worden ist.
This Basic Law loses its validity on the day on which a constitution comes into force, which was decided by the German people in free decision.
Artikel 146, new, after 1990:
Dieses Grundgesetz, das nach Vollendung der Einheit und Freiheit Deutschlands für das gesamte deutsche Volk gilt, verliert seine Gültigkeit an dem Tage, an dem eine Verfassung in Kraft tritt, die von dem deutschen Volke in freier Entscheidung beschlossen worden ist.
This Basic Law, which applies to the entire German people after completion of the unity and freedom of Germany, loses its validity on the day on which a constitution comes into force, which was decided by the German people in free decision.
Interpretational hint: The old version prepared for the situation when all Germans would be unifed in a single state again, the new version now states that all Germans are unified. Second hint: the GDR wanted the state of Eastern Germany as a final, real, nicely socialist state. They called their constitution just that: "constitution (Verfassung der Deutschen Demokratischen Republik)" accordingly.
As adopted by West Germany in 1949 as an interim constitution, the preamble of the Basic Law looked forward explicitly to a future free and united German state; "The entire German people is called upon to accomplish, by free self-determination, the unity and freedom of Germany." This was understood as embedding in the Basic Law both the proposition that Germany in 1949 was neither unified, nor free; and also as binding the new Federal Republic to a duty to pursue the creation of such a free and unified Germany "on behalf of those Germans to whom participation was denied".
The preamble and article 23 as well as 146 were changed in 1990. The Grundgesetz is now seen and serves as the de-facto constitution of Germany, as a complete state, containing all Germans and German lands that there are. The fact that the German people never did decide about a real constitution "in free decision" is an open wound caused by the decisions then that are now seen as final.
These conventions on interpreting the name and the meaning of the Basic Law was drilled and hammered into the heads of every pupil and student in West-Germany for more than 40 years.
Official order: Do not call it peace treaty, do not call it constitution
There were a number of concrete problems arising from this in 1989 and 1990. Simply expanding the territory via accession into the preliminary was also less complicated and thus faster. Polish and Russian territories were renounced in treaties before 1990 and offered as a pre-conditional renouncement for the unification process to the Soviet Union from the side of West-Germany before talks to these goals even began. Nobody in power wanted the German people to be so sovereign as to let themselves give them a real constitution, as required by the Grundgesetz itself, once all Germans are back in one single state. And in 1952 a little conference in London posited that West-Germany was given a break in paying war reparations to those countries it itself devastated as invader and occupier during the war. A break lasting until a "peace treaty would be signed".
When the merger was prepared the West-German government had precisely this in mind and wrote about this little problem explicitly and extensively in internal memos. They were so aware of this problem that they insisted in persuading everyone involved in the talks to not name this 4-plus-2 settlement a peace treaty. "Involved" means here the US, the UK, France and the Soviet Union, but all the other nations attacked by Germany and at war with it during WW2 were explicitly excluded from the talks, like Poland or Greece.
Treaty on the Final Settlement with Respect to Germany
The two-plus-four-treaty had the function of a peace treaty, but it was not called a peace treaty. This could not be in their interest "for financial reasons," said the German State Secretary Friedrich Voss at that time. The reason was the open question of German reparations for World War II, especially in the case of Greece. Today Berlin argues that the Greeks should have made their demands in 1990.
This came in handy during the last crises involving money and debt when Greece for example insisted that the reparations due, only promised to be postponed until after a real peace treaty, are due since 1990 and would help also somewhat now. The German government weaselled around to insist that until 1990 there was no peace treaty, and after 1990 they didn't need one anymore, since 2+4 served as such de-facto. Since Greece did not object to these talks and the treaty in 1990, when it had the time but not the chance (they were excluded from the talks) they were left in the cold on this to this day. ()
Germany is not a fully sovereign state. Among several other politicians that are on record with similar statements, this video showing Wolfgang Schäuble long-serving member of numerous governments, on Nov, 18th 2011, firmly asserting that;
"the whole idea is absurd […] we Germans have been, since May, 8th 1945, at no point in time fully sovereign."
This is true even now, since Germany relinquished some sovereignty in treaties regarding military to NATO, regarding economy and finances and law-making to the EU. EU-law breaks German national law. That is the stated goal of European integration. Even though Germany dominates the EU, and most of its decisions. This is sometimes costly for Germany. Germany wants his citizens to breath in diesel exhaust without limits, the EU forces Germany to adopt clean air limits in cities, even if that would entail prohibitions on driving dirty diesels, on certain days at least.
Given the fact that the US has bases in Germany that violate German laws routinely, the Reichsbürger point is only reinforced. The occupation by allied forces ended in the West officially in 1955, but the troops in Germany did remain unchanged in nature but in name. The 2+4-treaty, said that any occupation of Germany had now finally ended, again. But the troops remained. Only the Soviet/Russian forces really left Germany. French, Dutch, and especially British and American Forces remain stationed in Germany. Whether as occupiers or invited guests and military partners might lie in the eye of the beholder. German military bases in the US are allegedly quite rare to find…
Since the Reichsbürger also claim that the German Reich in the borders of 1937 is the aim of a true Germany it is also factual that large swathes of historical German land are supposedly occupied by Polish and Russian forces. As with almost all of their claims and aims, these ships have left the harbour now. The official Germany signed a number of treaties relinquishing any claims in that direction and promised to keep this issue untouchable in the future and really settled for good. These facts are of course just irritating the self generated reality of Reichsbürgers in which they chose to keep dwelling.
The Reich: new name, new management, otherwise buggering on in good health
These two claims from the question — most others they have do not — do have a solid basis in the history of the legal and political trickery from 1949 until now.
The central argument for the existence of Reichsbürger at all is for example much more outlandish, as they claim that the Federal Republic of Germany is not the legitimate, legal successor of the German Reich that collapsed in 1945.
While the Reichsbürger are again "somewhat" correct here, but the Federal Republic of Germany is not even the successor state of the Reich! In fact, the FRG is ruled as being identical to the German Reich, even if transformed, from 1871, from 1919 and from 1945. (Although again, there was some trickery involved for legal reasons in the interim):
Bundestag: Völkerrechtssubjekt "Deutsches Reich" (Auswärtiges/Antwort - 30.06.2015 (hib 340/2015)
Berlin: (hib/AHE) Das Bundesverfassungsgericht hat in ständiger Rechtsprechung festgestellt, dass das Völkerrechtssubjekt "Deutsches Reich" nicht untergegangen und die Bundesrepublik Deutschland nicht sein Rechtsnachfolger, sondern mit ihm als Völkerrechtssubjekt identisch ist. Darauf verweist die Bundesregierung in ihrer Antwort (18/5178) auf eine Kleine Anfrage der Fraktion Die Linke zum Potsdamer Abkommen von 1945 (18/5033). Die Abgeordneten hatten sich unter anderem nach der "These von der Fortexistenz des Deutschen Reiches" erkundigt und gefragt, ob die Bundesregierung diese als öffentlich als unhaltbar zurückweisen werde, "damit diese Behauptung nicht von Neonazis und der so genannten Reichsbürgerbewegung für ihren Gebietsrevisionismus gegenüber den EU-Nachbarländern instrumentalisiert werden kann".
The Federal Constitutional Court has consistently ruled that the subject of international law "German Reich" has not perished and that the Federal Republic of Germany is not its legal successor but is identical to it as subject of international law. In its reply (18/5178), the Federal Government refers to a small question by the parliamentary group The Left on the Potsdam Agreement of 1945 (18/5033). Among other things, the MPs asked about the "thesis of the continued existence of the German Reich" and asked whether the German government would reject it as untenable "so that this assertion cannot be exploited by neo-Nazis and the so-called Reich citizens' movement for its territorial revisionism towards the EU's neighbours".
West-Germany officially avoided to call the Basic Law "constitution" in order to amply its claims to be the sole rightful successor or the continuation of the German Reich, claiming all its former lands and territories in 1949. The official reasoning given at the time was that naming the provisional constitution "constitution" would acknowledge the final separation of Germany into two independent states and relinquish the rightful claims to former eastern territories. They avoided to call the Basic Law a constitution after 1990 in order to highlight that they technically violated the interim constitution's laws and provisions to explicitly create an entirely new and real constitution that would have to be subjected to popular vote in 1990, once Germany would be a unified sovereign state again in 1990. After the merger of 1990 they simply changed a few articles in the interim constitution to make it final. Germany also avoided to sign anything called "peace treaty", for a number of reasons, among them to avoid reparations for World War II as well as individual compensation claims, as was agreed to in the London Debt Conference treaty.
These wordings, policies, diplomatic manoeuvres and legal tricks provide the basis for the two claims in question. The German government, which the Reichsbürger do not recognise as legitimate, is their witness, ironically. The real government had other reasons than the Reichsbürger proclaim for doing what it did. The de-facto status of the Basic Law as a functioning and legally binding constitution is unchallenged in reality and most of the conclusions drawn by the Reichsbürger from this real conundrum of words are invalid.
The fact remains that this is extreme nitpicking of words and interpretations. But this nitpicking was deliberately begun (in 1948/49 to behold!) by the German government itself to avoid the proper words and procedures that were deemed necessary, evidenced by the original Grundgesetz –– and also by the international community as evidenced by the London Debt Agreement: having a constitution, having a peace treaty. In these two claims from the question the Reichsbürger have successfully found two points that are very complicated to explain properly and both points, when viewing their history, leave a shale taste even after explaining them and the situation as it is now.
Update, solely necessitated by some comments, please excuse the length; can be skipped, since the above should be sufficient, if read thoroughly, for the two claims called into question:
Since it was criticised in comments, apparently with some unfounded popularity: not all scholars agreed on the legal status of Germany or whether it ceased to exist, continued transformed or was founded anew, twice or thrice after the war. Just claiming the opposite is simply erroneous. There were several theories on how to view this matter, naturally also differing in emphasis between the West and the Eastern bloc. The West tending to assume continuation, the East favouring complete downfall. Please consider that each of the following theories had a number of adherents, rendering the shouting "all scholars" from the comments quite oblivious to history:
Rechtslage Deutschlands nach 1945:
Untergangstheorien, Debellationstheorie, Dismembrationstheorie, Fortbestandstheorien, Dachtheorie/Teilordnungstheorie, Staatskerntheorie, Kernstaatstheorie/Schrumpfstaatstheorie, Identitätstheorien
Ansicht der DDR, Ansicht der Bundesrepublik, Völkerrechtlicher Status
- Theories of downfall/demise, discontinuity, dismemberement: positing that the Reich ceased to exist:
- Theories of debellation: temporary occupation (Hans Kelsen: The Legal Status of Germany According to the Declaration of Berlin. In: AJIL 39 (1945), p. 518 ff.)
- Dismemberment theory: either with capitualation, founding of two states or at the latest with the Basic Treaty of 1973 the Reich ceased to exist and two entirely new states emerged
- Theories of continuity: The German Reich continued to exist but was incapable of proper function since the occupatio bellica.
- roof- or partial-state-theory: both West- and East-Germany were seen as parts of one Reich
- Core state theory: West-Germany remained the core of the continually existing Reich
- alternative core state theory: West-Germany or (East-Germany) was now seen as the fiduciary of the German Reich
- Core-State or Rump-state theories: either Germany was what remained of the Reich as the true Germany
- Theories of identity: West-Germany alone is the direct and unbroken contiunation of the German Reich of old. This became the de-facto view o most scholars and the current legal position of the government o the Federal Republic Germany as of now
Even some expert opinions on the different interpretations of the legal status of Germany after 1945, however moot they are now, could be read as lending some support for a few select Reichsbürger views and arguments.
As it seems, some need this disclaimer to aid in comprehension: This answer cannot be read as endorsing Reichsbürger views. This answer traces the origins and substance and validity of only two of their arguments. These select arguments are of historical origin and as such not completely without base and validity in history. All parties involved in the 2+4-treaty or the German merger of 1990 attempted some tricks, made sidesteps and mistakes. The Reíchsbürger views as a whole, describing the current status and implications and their conclusions from that, are no longer compatible with the current reality and should be viewed as a backwards oriented and dangerous political aim they have for the future.
Not fully sovereign:
Soverignty and international treaties, explained by the British Telegraph
The 1972 Act: supremacy of EU law explained
When the Parliament passed the European Communities Act 1972 it implicitly recognised the primacy of EU law over UK law - a principle that over the following decades was deepened and extended by the decisions of the EU’s top court, the European Court of Justice (ECJ).
Likewise the member states of international organizations may voluntarily bind themselves by treaty to a supranational organization, such as a continental union. In the case of the European Union members states this is called "pooled sovereignty"
Footnote 1: Wikipedia, GG: Der Parlamentarische Rat war der Auffassung, dass Deutschland als Staat der Deutschen noch bestehe und deswegen eine neue Verfassung für diesen Staat auch nur von allen Deutschen (bzw. ihren gewählten Vertretern) beschlossen werden könne. Weil die Deutschen in der Sowjetischen Besatzungszone (SBZ) daran aber nicht mitwirken durften, sollte zunächst statt einer Verfassung ein „Grundgesetz“ gelten. Dass nicht das gesamte deutsche Volk die Möglichkeit hatte mitzuwirken, dies aber noch tun sollte, wurde in der Präambel betont.
Bundeszentrale für politische Bildung:
Das Grundgesetz war eben keine Verfassung. Und es wurde auch nicht vom Volk in einem Referendum ratifiziert.