@Maggie ..... you have just said something highly pertinent .....

WH struggles to remember anything much at all about his childhood, and has major anger issues regarding his father.

I don't know whether it supports DID, and can't presume, but I believe Internal Family Systems runs a close example of how our personalities are made up of sub-personalities, and there is clearly something terribly wrong, but not obvious enough to the outside world (yet ?) to be able to call him out on it. To family and friends he is coming across as driven and eccentric I think, but relatively harmless to anyone other than himself.

Anyway ..... have to see what happens with the therapist we are seeing, one step at a time. It's clear to the team that is growing around our family that there is something fundamentally wrong.