SM, I'm so sorry i missed all this - it's so horrible.
I am feeling sick at your H's actions. It was not your fault, and i think his behaviour is sick and twisted. To make DS stay in his room as a reaction to YOU shouting, and undermining you, and wanting to keep ds prosoner, and having the temeerity to feel that he can, in effect, disciploine YOU by punishing ds is sick, cruel and deeply abusive.
It is outrageous that you have to live your life in fear of this horrible man and what he does to your children. Sweetheart, NONE of all that was your fault, and you most certainly are NOT a bad mum, anything but. But look how quickly he made you feel as if it was your fault, and you were to blame, and how afraid you were that he would make ds's life hell all afternoon. It sin't good for DS to see him weilding control and terrorising you like this, and for the poor lad to feel he has to re-assure you that he is ok, because he knows you have no control is very upsetting and worrying.That is no way to live, he is sick and twisted and cruel.
Sorry.
Can you ask your HV about getting legal advice, and maybe see a solicitor?
What would he do, do you think, if you upped sticks and said you weren't prepared to live in the house like this, and you are staying at your Mums for the rest of the hols???
I hope you can salvage some happiness with the boys this afternoon, but i know you will be chewing all this over and over in your mind - and poor you.
You deserve so much better.