I agree
The problem with these rabbit hole cases is it is easy to turn facts on the periphery of the case into 'castle in the air" theories. So where the kids are missing and no one knows where they are and LE can't find them, chances are they are not stashed with a death cult.
But on the other hand, once you get into one specific case, and away from making historical assumptions, the case can easily turn on its own bizarre and internal logic. So what might seem highly unlikely from the outside, is actually correct where all the facts point in that direction.
We just don't know enough about their motivations as we only have a few fragments of conversations to go on.
But in criminal cases, we infer intention from actions - and IMO there are strong pointers we can rely on, including a couple you identified there.
The fact that their scheme to start again in Hawaii doesn't make overall sense should not be surprising to anyone who has followed other sociopath cases down the years!