I don't want to disclose my specific relationship to this, but it's close and involved. Completely clueless as to best course of action.
Autistic adult son (50. very high IQ, but struggles in lots of ways) has very problematic relationship with parents (aged 80), in which he controls and monitors them heavily. Parents have always struggled with boundaries with him. Son has lots of mental health and physical health problems, is genuinely in a bad way, and is now saying he can't care for himself any more and needs to live with parents. Parents are offering a LOT of help (financial, practical, etc - right down to organising carers, etc, if needed), but he is saying the only thing that will do is moving in with them. They are 80 with their own health problems, and really cannot cope with being live-in carers (they are already carers for him in that they drop him food, do his laundry, organise his house; he lives locally). The man says that if he can't move in with them, he will kill himself.
(NB please don't suggest getting him sectioned. This absolutely cannot and will not happen. He know exactly what to say to whom. Also please don't suggest mental health support. He has accessed everything on offer and I don't think there are ant substantial unexplored avenues).
Any advice? Please remember that how the parents view him is as their vulnerable, deeply depressed child.