I’m sorry you’re in this difficult situation. I’m gonna be real with you.
You need to apply for divorce as soon as you’re able to. If you think he has left for good and won’t be back, don’t involve any authorities, that’ll bring complications you just don’t need.
HOWEVER, if you think he will be back, please contact the police non-urgent number now and make them aware of your situation should it escalate.
i am glad to hear of your housing situation, you’re very lucky. Just kick him out, divorce, apply for the correct amount of UC now he’s gone and if he says anything about seeing the kids (hopefully not!), do it via his mum, not directly.
try not to worry about the house, as long as the kids are sorted with food and clothes. You need to rest now, do the bare minimum. If you can, find time to stick toddlers in a nursery, it’ll be help a lot when the baby arrives (free hours).
in terms of recovering from birth, that’s gonna be tough but TEMPORARY. Think about giving birth and where the kids will be, could exs mother/grandmother have them for you. There are childminders who will be happy to help out for a week or so by having the kids overnight. Also can put up a post on local Facebook asking for help, local mums will help 100%, things like bringing homemade meals, nappies, etc.
I know it’s a lot, so don’t pressure yourself to do it all and at once. Think about you and your immediate needs plus the kids including the unborn baby. That’s all, the rest can be done later.
you’ll get through this