hi, I am sure your dh needs to move out before you can apply for yourself.
You need to ring child tax credits, and tell them you are now on your own, to get your claim looked at as a single mum.
Ring housing benefit, if you rent and tell them the same thing, so you can start your claim for rent help. If you are not working you will get it paid.
Ring Council Tax and say the same thing. you will get full help with that if you are not employed. You also qualify for a 25% discount.
Go to the jobcentre, or ring them to start a claim. You will be eligible for about £70, a week as long as you are not living with your dh. You won't have to start looking for work until your youngest is 5 yrs old, and only then you can limit it to school hours, or something that firs in.
If he is working, then he needs to pay child support, which you can calculate on the csa website.
This money can be arranged in a private arrangement, or you can apply to get it out of his wages.
New rule a couple yrs ago means that you can keep all your child support, it used to be you were allowed a tenner.
hth