Offering a hand hold .
And some advice:
Get to grips with the family financial situation. Find all documents relating to bank accounts of all sorts, H's pay stubs, investments, mortgages, CC bills, car loans, rent.
Who owns the family home?
Are both names on the deeds?
If renting, whose name is on the lease?
Hire a solicitor.
All of this needs to be done asap.
There is never a good time to go through the process of divorcing, but a bad time to go through it all is before you know all the details of the family finances.
Explore with your solicitor the options you have wrt custody and visitation/ facilitating the involvement of both parents in the lives of the children, and how your preferences can be amicably achieved. Discuss the ramifications of each option when it comes to deciding what is to happen to the family home if owned, not rented.
Have you told your parents, siblings, friends? You uneed to ask them for support. Don't hesitate to ask them for specific sorts of support - child minding while you go to see a solicitor, a home cooked meal from someone, a grocery delivery. Cash (and lots of it) if you can't afford a solicitor.
You and H need to sit down together and discuss how you will break the news to the twins. They need to know that this is a decision mum and dad have made because of mum and dad's feelings, NOT because of anything the children have said or done, that mum and dad still love them to bits and are proud of them, and will always be their loving parents despite living apart. Assure them that their birthday will still be celebrated, that all the other holidays they love will still happen, though maybe not in the familiar way.
If dad has started a relationship with someone else he needs to be honest with you so that the two of you can prepare the children for an introduction to the lady or gentleman in question (in good time, no hurry here - this needs to be negotiated and accomplished with the children's best interests in mind).
If the family home must be sold, then that is another horrible conversation with the children. But talk to a sol wrt your rights and how different custody scenarios will affect the disposition of your home.
You need to ask your H what his plans are - when will he move out, where will he be living. He owes you that information.
You need to talk to a solicitor about an interim financial support arrangement until the divorce is finalised (if he earns more than you do).
This is a horrible thing to have dropped in your lap, but please talk to your family and friends and ask them for support.