Why would you be shocked if he didn't want them 50/50? Look how he behaves towards them now. You'll be lucky if he has them every other weekend, and 1 night midweek (which is the usual arrangement). Plus, I can't imagine your children would want to spend that time with him, if all he ever does is shout at them.
I don't mean this as an insult, but you sound very naive. I suggest you have a read of the threads in the Relationships part of the forums. These men often threaten their wives/partners with taking them to court to get custody of the children, but it's all bullshit. They're just using it as a threat to keep the woman too frightened to leave, because they don't want to have to live on their own, doing their own washing, cooking, cleaning etc. When the women leave, it's actually the other way round, it's them who have to take their exes to court, to get them to have the children at all, and pay maintenance.
Go and see a solicitor to find out what's involved, and what you will be entitled to in a divorce settlement. Often, you would stay in the house, until the youngest child reaches 18.
Log on to the entitled 2 website to find out what benefits you will be able to claim, and roughly how much you'd get.
Look at the bills, to see how much they cost each month. (As a single person, you would get 25% discount on council tax.)
Start putting some money away if you can. Save £2 coins (they add up surprisingly quickly), get cashback at the supermarket, do some surveys with survey sites that pay you. They don't pay a lot, but every little bit helps. (Check Moneysavingexpert.com for the best survey sites.)
If you do all these, you will feel more empowered, because you've taken away some of the unknown that you're frightened about, and you'll have some funds behind you.
It's really not good for your children, or you, to be living in this toxic environment. It affects self esteem, and children are very vulnerable to this.
It really is worth it. That feeling of happiness, relief, etc, will be every day. You'll no longer feel your heart sink when you hear his key in the lock, nor walk on eggshells around him, to try not to set him off.
I remember that feeling well, and the feeling of relief when we split.
I wish you all the best.