Brother with autism needs help?

TheMy brother has for awhile started to think that my father has been lying and everything that doesn t go his way is our fathers fault. He keeps saying he deserves to go on the street and should never have existed or should die and that he s a terrible person. He keeps blaming him for things and yet he says he doesn t remember anything that my father did wrong. I am concerned because this is really tearing them up and my father is a wonderful man. He is patient and is often the one trying to help squeeze things in for him so he can see all his friends.
What can we do to get him better???