Re: I asked him to move out.
Tell his parents the truth, but ask them to be supportive of him. Your not looking to damage their relationship, but if another relationship of his fails in the future, at least they will have an inkling of why. You can be both honest and take the high road. You should also cut contact with his family. Sure biological bonds tends to be stronger than one's by choice, but it does not mean that it will not cause conflict. Tell his family it is over, and there is no going back. Ask them to be there for him as he too, is going through a difficult time, and ask them to see if he can get some help.
After this, keep contact to text, email, or anything else that is recordable. You want to play smart, and if his text is abusive and derogatory, you have something to show people the type of person he is. Tell his family that as much as it pains you, you need to cut contact with them as well.
I am such a tree hugger because it gives me wood!