I agree with the OP about nurseries, while I don’t agree each and everyone is the same there is a large quantity which are this way. My friends children have had these experiences and were unable to go back to the nursery, they decided to wait out until their child started school. I have also witnessed it first hand, so I understood your worries OP.
The way some of you are writing ‘the fact that you’re prepared to continue put your children through this’ OP has been clear that she has been threatened. The first step was coming here for support, it is extremely difficult if you are living in fear for yourself as well as your children. It’s clear that OP has a limited range of options, from what I can see is you’re going to have to get some sort of enforcement involved. As horrible and awful as it is, it’s going to allow you to make space to leave. Women’s aid a previous poster wrote about may be a great option, you will have to get legal authorities involved to stop visitation for the kids to go to his mothers you said? While I can see from your post it isn’t something you want to do. I don’t think you have any other option.
He has decided to take this road, the consequences should be his own. As much as you may not want to hurt his family, or even him because his is the father of your children. (I’m not saying he doesn’t doesn’t deserve to be hurt) But he’s made these choices himself, if he wanted to be a real part of his children’s lives, of your life. He could quit the drugs, get help, return to education and better himself, even with his learning difficulties.
You doing a masters amongst all this, is incredible. See it through, as hard as it is. You’ve got this. In regards to the 2 year old, finding a good nursery may be difficult but do your research and talk to those around your area of their experiences with the nurseries, you have given 2 years out of a nursery setting. It is a year before DC will be able to go to a school setting in reality that isn’t a long time.