1- Know that it has nothing to do with you. you are not at fault and there should be no guilt
2- Put his name in teh Bracha of Refainu because he needs a refuas hanefesh. that will reinforce within you that he is not well……. a ruach shtus has entered and needs to be dealt with by THE ROFEH!
3- Find a warm caring private understanding person to talk to so you can vent without causing your parents more pain.