Your husband needs to move out right now. You and your children need to be safe in your own home.
Contact your husband at work and tell him to not come home. He needs to move elsewhere . Make an arrangement to drop his stuff off. Don’t let him come to the house to collect it.
Holding your son around his head and neck so he can’t breath is potentially life threatening. Your son needs to go to A and E today so they can check his neck and throat for any damage. It’s not always obvious from just looking at him.
Once he has moved out, your husband can access any individual therapy he chooses.
Family therapy is not appropriate where there is abuse - in fact any reputable agency will refuse to do so as soon as you tell them that your husband is verbally and physically abusive.
What ages are your children ? It sounds like they both need some professional help.
I know you are reading my post and thinking that I’m over reacting, that a little chat will sort this out. That your husband realises that he’s “ gone too far this time”.
No he doesn’t. It’s not an issue for him , he says there’s nothing to talk about. You are busy excusing him saying that he’s “ volatile “ and his mother is ill. But he’s been like this for years hasn’t he?
You can’t fix your husband . You and your children are at risk. Your children are already traumatised, your son is possibly physically injured . Your children at at risk of going into the care system unless you put then first and protect them.
You ask in your OP “ What do I do now? “. You need to choose between staying with your husband and keeping your kids safe.
You can’t do both. I know you want to with all your heart. But you can’t.
I’m so sorry.