TM7, by all accounts the IDF did not board them for suspicion of "commandeering war supplies." They boarded them for failing to comply with a blockade ... that's the fork in the road for you and me. All other assumptions are predicated on why you think they boarded.
You've not given me any forensic evidence that the 2 shots preceded the boarding; could they not have occurred after hostilities began? Does the autopsy corroborate the time, distance, and angle of fire matching the witnesses claim? I've not read that. Without it you can't prove either way.
The autopsy shows shots to the back of the head, but no powder burns at the entry point, and in conjunction with other shots on the front of the bodies as well. In no battle damage assessment would that be sufficient to declare an "execution." Were the bodies found on their faces, with zipties on their wrists, brass casings 2-3 feet behind their shoes, lying together? Were the bullet holes uniform, i.e. placed in a similar location indicating controlled fire. What is the evidence that makes this an "execution" and not just a shootout? Read a BDA from a shootout, or watch the history channel on any of the wars we fought with firearms - lots of folks with wounds in the back of their head. Some while turning away having just been shot in the front.
Give me the corroborating evidence, and I'll buy it. I stated up front, I'm only discussing the operation, not the validity of the blockade. Just the what happened. Both sides have motive to lie to some degree, so to determine what happened you have to set motive aside and disbelieve everybody. I've done critical incident stress debriefings with teams that were in close quarters kinetic engagements, and so far all the data I've seen from both sides, this was a terrible event, that no one should feel good about.