I don't believe any of the parents had anything to do with Kyron's disappearance. My dominant theory is that he was taken by an opportunistic predator.
I do, however, agree with others that activities going on the parents' lives, Terri included, greatly complicated this already complicated investigation.
For me, I've never cared about being right or wrong about this. I don't really care if Terri is guilty or not. If Terri is guilty, then I want LE to prove it so that Kyron can be found. My issue with this case is the complete, IMHO, mishandling of this investigation. For me, it's always been clear that LE was hyperfocused on Terri with very little corroborative evidence to support their assertions. I think others may have had resentment against Terri, and Kyron disappearing gave people an opportunity to vent their resentment, rage, etc. against her.
She may have been a little off, or grieved differently, or maybe she's mentally ill, who knows, but I think LE used superficial actions to try and fit her into the perpetrator role in this crime, and she just doesn't fit, IMHO.
I hope that whatever happens and whoever is responsible, Kyron is found.