I wanted to post something similar to Flop. I found it difficult to express what I was thinking without seeming like I'm minimising your fears about your DC. Nor do I want to suggest you should put them at risk or accept that contact is inevitable.
I completely get where you are coming from. You don't have to be around long on the relationships board to appreciate contact is often an issue post separation.
But some thoughts if your fears are right...
You intervene when he behaves badly with DC - but you cannot stop things happening. The reality of the status quo is that you can't fully protect the DC because you can't control his behaviour. So you aren't comparing "contact" with a perfect current situation. They live with him and his behaviour every day. if you left you would get them out of that for at least the majority of the time.
Are you the best "you" living as you are? Imagine how great a mum you would be living in a tension free, abuse free happy household. A home where you are not disrespected, where you parent as you see fit, where you can create a loving calm environment. If you left you could give your children that happy home for most of the week.
Sometimes when dads only see their children every other weekend the children get the best of dad. The time is novel - without the daily grind, might he be able to muster up a decent stab at parenting every other weekend? Might there be less cause for him to be impatient, snappy, angry etc.
Perhaps you can't stop contact but can you do enough that he might be more concious of how he parents? If he knows going to court is a possibility, that you have spoken to a solicitor or any other professional about his behaviour and your concerns, might he realise that needs to keep his issues in check with DC?
If you left there are people you could look to for support, eg, nursery staff or school will take it seriously if you say to them that DC are going through huge upheaval, can they keep an eye on behaviour etc. Then there would be others who are looking out for their well-being.
Just some things to think about. I know how it is to feel stuck. A year ago I had a user name with "stuck" in it. I wasn't though. Maybe there are other people to talk to? Perhaps WA again. Or your local domestic violence organisation? Or take up free initial meeting with family solicitors? You've started questioning it, keep thinking and keep talking.