this is the thing that would work for me every time:
YOU OWE IT TO YOUR CHILDREN TO LEAVE.
You will either be killed or viciously abused if you stay in this relationship. Either one of those things will hurt your children so much. I AM NOT saying this to make you feel bad. It is not your fault. I am saying it because I am afraid for you and you are a mother and I am trying to say it in mother-language.
PLEASE the very next time YOU AND YOUR CHILDREN are out of the house OR he is out of the house and will be a significant amount of time i.e. the start of a work day - children home from school "sick" with a tummy bug, whatever - call the police. Say you are in danger. Tell them what you have told us word for word and ANYTHING YOU HAVE LEFT OUT FOR FEAR OF EMBARRASSMENT.
Delete all your net history, including recycle bin. Plant false history in it by clicking on loads of sites for just one second so it doesnt look suspicious. And be as nice to him as you normally would, no more, no less. But be submissive. And lie through your bloody teeth as if you and your childrens lives depended on it. Fool him into thinking you are maintaining status quo but no matter what protect yourself and your children by legally and physically removing yourself from him. You will need a restraining order.
I am sorry to be so damned extreme in my posting - I am usually a fairly reserved person and try to see all sides - but if what you say is true and I believe it is - you and your children are in danger and it makes me afraid for you. Please please please call the police, call the women's aid people linked to earlier and again, lie to him. Make him comfortable until you can safely get out. Please let us know you are ok and what you are doing.
I am sorry if anyone thinks I am being too extreme I got a real gut feeling I had to post this exactly as I have done.
I really hope you and your children are ok. And please, give yourself a break. You are not responsible for all this and you can still turn it around.