The first of the lethal bombings listed in the OP has a Wikipedia article, Church Street bombing (20 May 1983), which says,
In submissions to the Truth and Reconciliation Commission (TRC) in 1997 and 1998, the ANC revealed that the attack was orchestrated by a special operations unit of the ANC's Umkhonto we Sizwe (MK), commanded by Aboobaker Ismail. Such units had been authorised by Oliver Tambo, the ANC President, in 1979. At the time of the attack, they reported to Joe Slovo as chief of staff, and the Church Street attack was authorised by Tambo.
TAMBO ORDERED CHURCH STREET BLAST: ANC says that people other than Nelson Mandela were responsible for this action.
Mandela was captured in 1962 and imprisoned until 1990.
While he was in prison, he did not "reject violence":
in February 1985 Botha offered him a release from prison on condition that he '"unconditionally rejected violence as a political weapon". Mandela spurned the offer, releasing a statement through his daughter Zindzi stating "What freedom am I being offered while the organisation of the people [ANC] remains banned? Only free men can negotiate. A prisoner cannot enter into contracts."
But I find it implausible that he had any personal control over tactical or strategic decisions taken by people such as Oliver Tambo, during the period of the lethal bombings of 1983 through 1988:
In April 1982 Mandela was transferred to Pollsmoor Prison in Tokai, Cape Town along with senior ANC leaders Walter Sisulu, Andrew Mlangeni, Ahmed Kathrada and Raymond Mhlaba; they believed that they were being isolated to remove their influence on younger activists.[160] Conditions at Pollsmoor were better than at Robben Island, although Mandela missed the camaraderie and scenery of the island.[161] Getting on well with Pollsmoor's commanding officer, Brigadier Munro, Mandela was permitted to create a roof garden,[162] also reading voraciously and corresponding widely, now permitted 52 letters a year.
Recovering from tuberculosis caused by dank conditions in his cell,[173] in December 1988 Mandela was moved to Victor Verster Prison near Paarl. Here, he was housed in the relative comfort of a warder's house with a personal cook, using the time to complete his LLB degree.[174] There he was permitted many visitors, such as anti-apartheid campaigner and longtime friend Harry Schwarz.[175][176] Mandela organised secret communications with exiled ANC leader Oliver Tambo.[177]
Regarding his activities before he was arrested, one of the blogs referenced in the OP (which I viewed as a questionable 'claim', not as 'evidence') said,
In fact, it is still a mystery why Percy Yutar (the then state attorney) did not file for murder, but manslaughter instead. Based on the facts it is commonly agreed by legal scholars that Mandela would have been hanged if Yutar filed for murder.
This article on Wikipedia says that "some deaths did occur" but without details or citation (so perhaps, in its present state, it's best ignored):
Nelson Mandela, who was the commander of MK, had developed the "M Plan" (Mandela Plan), a programme of controlled sabotage, launching a guerilla war modelled upon the FLN's struggle in Algeria. Its policy involved the targeting of state buildings for sabotage without resorting to murder. On 16 December 1961 MK carried out its first acts of sabotage by assaulting post offices and other structures in Johannesburg, Port Elizabeth and Durban. Many other acts of sabotage would take place over the next few years. In its first eighteen months, MK carried out about 200 acts of sabotage, but despite its policy, some deaths did occur.[citation needed]
I found a credible reference to one death/killing in The Nelson Mandela (Rivonia) Trial: An Account, which says,
Justice de Wet turned to Bram and announced in a gentle voice, "You may call your next witness." Walter Sisulu, former Secretary General of the ANC and a member of MK's National High Command, took the stand. Sisulu testified that Operation Mayibuye was the brain child of Arthur Goldreich, a member of the High Command and a former member of the Israeli underground movement. Sisulu said that the plan had not been adopted, in part because more time was needed "to condition the masses." The ANC and Umkhonto, Sisulu also told the court, were separate organizations. He testified that he agreed sabotage was necessary, but insisted that "the choice of targets makes the position perfectly clear that the intention was not to injure anybody at all." Pressed on this point by Justice de Wet, who pointed to the death of a passer-by when a bomb exploded at a post office, Sisulu conceded that accidents could happen, despite the precautions Umkhonto tried to take. In five days of cross-examination, Yutar tried to link the ANC and Umkhonto to the Communist Party and pushed Sisulu to identify others who played key roles in underground organizations. Despite warnings from the bench, Sisulu refused to name names.
I see no evidence that they were tried for even manslaughter:
- [...] prosecutor Percy Yutar called the case of "State versus the National High Command and Others." He then produced an indictment
charging the eleven defendants with two counts of sabotage and two
counts of conspiracy
- Defense attorney Bram Fischer led off the proceedings with an attack on the sufficiency of the indictment. He argued that the charges were
vague, and failed to provide any indication as to which defendants
carried out which alleged acts of sabotage. Instead, the government's
indictment simply stated that details concerning the sabotage were
"peculiarly within the knowledge of the accused." Justice de Wet, in
his flowing red robes beneath a wooden canopy, found the defense
arguments convincing. He told Yutar that the indictment seemed to
presuppose guilt and provided almost no clue as to the nature of the
offenses. The indictment, Justice de Wet announced, must be quashed.
- In December, the remaining defendants were back in court to hear Yutar read the state's new charges. The defendants were accused of
sabotage, ordering munitions, recruiting young men for guerrilla
warfare, encouraging invasion for foreign military units, and
conspiring to obtain funds for revolution from foreign states.
- [...] later, Justice de Wet announced his verdict. Only Rusty Bernstein was acquitted. Ahmed Kathrada was found guilty on one of
the four counts. The other defendants: guilty on all counts. Justice
de Wet told the assembled courtroom that he would deal with the
question of sentencing the next morning. He released a 72-page
summary of the evidence with findings. Justice de Wet concluded,
among other things, that "beyond doubt Nelson Mandela had been the
leading spirit behind the creation of Umkhonto we Sizwe" and that
"Operation Mayibuye comprised a detailed plan for waging guerrilla war
intended to culminate in full scale revolt against the Government of
South Africa."
There is evidence that the High Command of MK had at least been considering future guerrila warfare: Operation Mayibuye.
There's reason to doubt that Mandela personally endorsed this plan:
- Sisulu testified that Operation Mayibuye was the brain child of Arthur Goldreich, a member of the High Command and a former member of
the Israeli underground movement.
- The defendants contended that Operation Mayibuye had never been formally adopted by the High Command and was merely under
consideration as a possible plan of action. Mandela later described
Operation Mayibuye as a "draft document" that he considered "entirely
unrealistic in its goals and plans." Operation Mayibuye was drafted
by members of the National High Command. Mandela, who was imprisoned
at the time, did not participate in drafting the document.
The closing statement from the defence helps to explain why the defendants (including Mandela) were neither tried nor convicted as 'killers' (including "murder, incitement to murder and attempted murder"):
May it please your Lordship, the State has told your Lordship that this trial is a trial for murder and attempted murder. The indictment alleges military training and sabotage. But despite this the accused have been subjected to cross-examination on murder, incitement to murder and attempted murder. The evidence presented to the court on these claims is all hearsay, and the existence of these claims has never been substantiated in this court. There has been a mass of inadmissible evidence which bears no relation to the indictment. The defense will not even deal with these allegations as they have nothing to do with the case. The defense concedes that Umkhonto we Sizwe recruited men for military training and that members of Umkhonto committed acts of sabotage. The defense denies, however, that they committed all the acts of sabotage with which they are charged. I will demonstrate to your Lordship, from the evidence, that there were other organizations in South Africa committing acts of sabotage at the time in question....
Even if the State had succeeded in proving that certain acts of sabotage were committed by Umkhonto, that is not the end of the matter. The accused who the State said were the leaders of Umkhonto are only responsible for the acts falling within the designated policy of Umkhonto. The evidence is that Umkhonto’s policy was only to commit acts of sabotage against government and public property which it labeled symbols of apartheid. The evidence further shows and stands corroborated by the evidence of the State witnesses Mtolo and Mthembu that the clear policy of Umkhonto was sabotage without loss of life. The authorities show that if one member of the conspiracy goes out and commits an act falling outside the ambit of the conspiracy, his fellow conspirators are not legally liable for such acts. On this basis the accused, who adhered at all times to a policy designed to avoid danger to life, were not responsible for acts of sabotage committed even by proved members of Umkhonto against their instructions. The accused accordingly disclaim all responsibility of bomb attacks on private houses...
IMO the evidence suggests that:
- They deliberately avoided killing
- If anyone were killed, that was by accident; or against their orders; or independently (not on their orders at all).
- Some of the MK High Command (Mandela was arrested and imprisoned before the others were) considered escalating, in the future, from sabotage to guerrilla war.
I don't know what Mandela's own views, intentions, or actions were re. a hypothetical future guerrilla war, civil war, and/or invasion of South Africa by foreign armies.
In summary the evidence suggests that Mandela's actions and intentions were not "non-violent", but he was not a killer. In his own defence, he wrote,
Firstly, we believed that as a result of Government policy, violence by the African people had become inevitable, and that unless responsible leadership was given to canalise and control the feelings of our people, there would be outbreaks of terrorism which would produce an intensity of bitterness and hostility between the various races of this country which is not produced even by war.
