So very sorry op, all l can say is for the sake of you and your children you HAVE to get away from him but you know that.
There are a lot of things you can use against him, ie previous documented abuse/illegal subletting/benefit fraud.
If you are sensible you could end up with him in prison, or at the very least fighting so many other problems he has no time to harrass you whilst you get yourself and DCs away from him.
Now is the time to get finances organised, stop saying you are rubbish, you are quite capable of drawing up a simple budget of how much it costs you to live with the DCs if he was not there,
List your expenses, as if he were gone, then see if your salary will cover them.
Check what benefits/tax credits you may be entitled to ( do it in your work lunch break if you have too, but do it immediately) You really need to know how much you will have if he is gone.
Open a new bank account if he has access to yours, tell no one.
Can you get a tiny camera and record the verbal abuse? Hide it in an ornament?
Get proof of the illegal subletting, documents / photos / payments into bank etc
Get a video or photos of him attending the martial arts club, even if you have to get a friend to do it for you.
Put these photos and documents in a P O box, tell no one you have it.
Google fake/toy passports, you can get fakes and swap them, put the real ones in the PO box, unless he is the sort to check closely, which sounds unlikely.
See if you can get a week or more off work, explain your circumstances if necessary, and plan to go somewhere for that time, somewhere he cannot find you and Dcs, if you explain to their school there won't be a problem.
Organise totay with a friend perhaps, one he doesn't know, or if finances allow a very cheap holiday camp.
If you could get all this done you are almost free.
Just wait till he is out of the house, go with Dcs on your escape, then spill the beans on him to the police/ Benefit fraud office/ Call SS etc.
Arrange in advance to have the locks changed.
Call in some male friends to be there when you return too, and be prepared to call the police at any time.
Good luck op, please get him out and stay safe.