Your husband is under their control. Very similar to those in a cult. The same brain washing takes place.
His family have abused him, controlled him and continue to manipulate him so he becomes confused, it is very disorienting. He needs urgent professional help.
Your dh doesn’t know this is happening, because he doesn’t recognise it as abuse and manipulation. He will live in fear that they will abandon him, he is very, very damaged op. Perhaps you didn’t understand the extent of it, or the impact it would eventually have when you met him.
Stand firm on this op, or your life as you know it will be over. Everything you have said is entirely reasonable and fair, but he won’t be able to see it that way for now.
You did the right thing moving so far away, it was the best chance you had as a family but it’s now under threat, it is being directly challenged, and he seems unwilling and unable to defend you or your life together. Do you have real life support? Close friends? I think you need some help and support in real life op, what you are uncovering now is huge.
The plaster has been ripped off, and now you can see the gaping wound it must feel very frightening to be in this position.
First things first. Prioritising the children with their revision. Keep everything calm and quiet. Nothing will happen immediately anyway,
Secondly, take a long hard look at your finances, get everything in order op. Take legal advice so you are aware of your position. Ensure you have copies of all paperwork and passports etc are safe.
Maje a plan B based on the worst case scenario. What does that look like?
You need to tell him clearly and directly. This IS a dealbreaker. If he chooses his mother over you, then that is his choice to make, hut you will no longer tolerate being bulled by her or be forced into any living arrangements that will be severely detrimental to your children. He needs to know he could lose everything.
I am so sorry it has come to this.
I would add that he isn’t welcome back until he has booked a professional therapist. It’s absolutely toxic.