Who owns the house? His daughter?
Are the DCs all his?
Do you work or have any tax credit child benefit income?
Do you have your own bank account?
Are you in any physical danger?
Does DP know you want to leave? Is he likely to be obstructive? Do you want to stay local? What about schools/family friends support?
You can go to cab or similar to get a benefits check to see how much you'd get when you leave.
Find out what the local council/ housing association waiting lists are like. Find out what size you'd be eligible for depending on ages/sex of DCs.
Would you expect regular contact with DCs after break up? What about child maintenance?
Look into private renting and see what is available and at what price.
Who could help you with the logistics of moving?
Do you have all your and DCs important documents eg passports/ birth certificates? Could you give these to a local friend for safekeeping?