You didn't cause it, you can't control it and you can't cure it.
(((LovingMom)))
Hate the sin, love the sinner...you know the drill. Stand your ground. Support your D-I-L, maybe get her to al-anon and help her find some dv info in her area. Urge her to get a restraining order and to let it stand until he's clean and sober and has his anger in check for a good long while before she even considers dropping or amending it. Get every member of the family on the same page...no enabling. Love Sonny Boy but allow him to be responsible for all his own actions and all the consequences they bring.
This could be your HP opening a doorway...letting the sun shine upon Sonny and holding Sonny Boy in the spotlight so he can realize the impact of his actions. This could be his hit-bottom-wake-up-call.
(((Loving Mom)))