What would happen? Well you might get some support, I think it would work entirely in your favour. There's no court order so he's going to be disappointed to find he has no power to stop you leaving and taking the children with you, or power to force you to come home or send them home, you aren't actually his possessions. Social services or the police might contact you to see if you're all right - whereupon you get to explain you're being coerced, harassed and intimidated by an abusive twat and afraid to go home/sleeping with the kids in a locked room, and show your texts from him and his request for invoices. I think after that they might talk with you about how to get further away from him and add quite a bit to your DA evidence.
He can go to court if you leave permanently with the children and he wants to press it, but you then pull out your evidence and explain to the judge he doesn't have one screw fully tightened. And the judge will then negotiate a court order about contact, which I suspect will take his parenting skills a lot more into account more than he will like.