this is not the way to bolster and support a mother in an abusive environment. Yes I am as frustrated as you that she doesn't want to call the police, but it's a scary thing to do. For her she feels it has ramifications.
ThankYou: My love. You know what situation you are in. You know it's unhealthy for ALL of you. Your children are being directly exposed to domestic abuse. In the eyes of SS, they would be classified as being abused themselves.
This man is abusive, classically so. He will eventually hit you and the DC. He has already smashed stuff up, and is expecting you to clear it up. DON'T.
Get yourself, and the DC, RIGHT NOW and go to his mothers and TELL her what he has done. Tell her that it was either you go to her, or that you call the Police. I still think you need to do that, to log the event, to start to compile the support you WILL need to protect yourself in the future.
Your MIL needs to call him and tell him to make the house safe for her GC. I don't think he would take it from you.
Then you need to start coming around to the idea that things WILL get worse, and worse and worse. They will never get any better.
Please understand that this is nothing YOU have done, will ever do, think, say, feel. None of this is about you ThankYou. This is HIS choice to abuse his family.
You have to protect them, at worst he will recruit your DC and use them to abuse you more, or he will directly abuse them. OR your DS will grow up and abuse HIS WIFE or his children. Literally the only thing you can do now is to save your DC, and yourself, and the only way to do that is to find the truth in your head which is to LEAVE.
Be careful, when they know you are leaving is the most dangerous time. You could be killed, your DC could be killed. It is THAT serious.
Call Women's Aid for help, RL support and advice how to get out. There IS no plan B. CAB can help you WRT to benefits/help etc. Please use every single resource there is to GET OUT.
Please? For your DC? for YOU?