I was actually talking about this with my friend at work today! It really is an interesting situation, and I'm in very split minds about it.
On the one hand, I can't see why these two men would come forward with their stories when there's really no incentive of fame or money in it for them. If anything, if all they wanted was money it would be smarter for them to take his estate to court and try and make some money out of a lawsuit instead of signing onto a documentary which I don't believe they got paid for.
On the other hand, the FBI conducted a criminal investigation into MJ for over ten years and didn't find any evidence to charge him with. Given that this was such a big case and he was such a famous man, I can imagine they would have been using every tool and worker at their disposal in order to find some kind of evidence, so the fact they didn't should say something about his innocence.
Either way, I question if there's really any point for me in watching the documentary. Michael has been dead for many years and he has no ability to defend himself against these claims. Given that he's dead and the two guys really have no way of proving things one way or another, all this documentary is really doing is upsetting people and destroying their positive memories which may be associated with his music.
With that said, if I had to go with my gut instinct I would guess that he's guilty. These rumours have been going around for as long as I can remember, and I would have to imagine that where there's smoke there's fire.