Your dad has dementia, or something close to it. I' sorry to say this and i'm putting myself out on a limb saying this, but from what you have described, there leaves little doubt of the outcome.
A PWP who does not have dementia does not have such a significant personality change such as you've described. If your mom feels the way she does after so many years of marrriage, then he does have a problem.
Best to get him some professional help. This will avoid both him turning violently on you or you marginalizing him because of his anti-social behavior. This is one of the BIG usually suppressed problems with PWP; especially the elderly. There is no excuse for your father to treat you and your family this way, but remember he doesn't mean it; he just doesn't know what is happpening to him. Don't sweep this under the carpet, it will only get worse. With time and counseling, there is a chance that he may learn that his behavior is wrong and he may be able to put a lid on it, for all of your sakes.
I am sorry to hear that he has turned this way on your family. It is very diffiicult to deal with and a burden on ALL of you.