is your son able to ask the doctors if he can have a brain scan.
if his behaviour has turned so suddenly out of character, surely all possibilities must be investigated.
don't let them palm him off on to you. thy will probably say he is just a dirty old man, family disputes, blah blah.
but this situation sounds much more serious than that.
he is volatile, and deluded, and doesn't like you standing in his way a he sees it.
please don't have him home.
if you absolutely cannot stop it, you need to go elsewhere.
do not be alone with him.
there was a terrible case near here a few years ago; a woman said her husband was not well or stable enough to be discharged from mental hospital, but they insisted, told her to contact GP. who was closed when he came home, she tried other sources of help, was made to feel that she was being overly demanding, told to ring GP when open.
he came home in the evening. early the following morning, the milkman found her slaughtered on the doorstep.
after that they found a place for him to be detained. bit late.