Ok, so practical head on.
Get as much stuff together as you can paperwork-wise. Get yours and the kids passports together and keep them safe, away from the house if you can. Also, get a bag together of the essentials, a change of clothes for you all, bank details, ID, a copy of your housing tenancy/mortgage, a recent bill (for ID purposes) etc. and keep that somewhere safe too. Anywhere that you can get it quickly so a friends, your mums, a left luggage locker, anywhere where he cant get a it.
Then, again when you can, take copies of bank statements including any savings accounts/ISAs etc, copies of bills, credit card statements, debt payments. Try and keep these as up to date as possible. These mean that a) you can prove who you are b) that you have rights over your property and c) if you do leave him that you have proof of his income and assets in case he tries to stiff you over maintenance for the kids.
You can do this. If not for yourself but for your children, they deserve better than this xx