As far as I can tell the only source named making claims such as these is Moshe Elad, who is identified only as a "lecturer at Western Galilee College and at Galil International Management School". I believe he is the same Moshe Elad who co-authored a "hasbara manual" in 2010. Hasbara is Israeli government public relations, so this indicates to me that Elad sees his own expertise as related to national PR.
In 2014, Elad made this claim in Tablet magazine, citing "my research," and for the New York Jewish newspaper Algemeiner, citing unnamed "Arab commentators" and "global estimates."
Here is a list of claims made by Elad and by Channel 13, respectively.
||Channel 13, 2021
|Mousa Abu Marzook
It should definitely be noted that Elad made these claims in the midst of the 2014 Gaza war in which Israel killed over 2,000 Gaza civilians, and the Channel 13 claim came out directly after the 2021 Gaza war which involved killing of civilians in Gaza and pogroms against Arabs within Israeli territory.
edit: In response to comments: the goal of this answer is to clarify who is making these claims and where the claims have arisen. I did not find other sources for the net worth of Hamas leaders, and I welcome such discoveries, but I believe this supplemental information by itself can help people draw a conclusion.