Honest question: were the children merely trying to cut the self-titled fiancé off? As adult children might if a gullible parent were being catfished online?
Dia strikes me as a generally trusting person. Kind, good-hearted. Perhaps the children feared she was being taken advantage of and Dia felt it was controlling and unwarranted, assuming instead the best of people's intentions.
Maybe I'm way off but I don't feel like the children were trying to take it away from her so much as they didn't want him to get it.
Imagine if Dia was simply trusting. Didn't think someone who was so helpful had greedy, untoward motives. Her children saw red flags that she did not, creating tension between her and them. And nobody dreamed the worry was well-founded and that situation was fast on its way to deadly.
I think it's very possible that Dia was restrained, sedated, and removed from the property alive, only to be discarded after a long drive to a remote location.
Who saw Dia last? Start there.
Finish there.
Jmo