My parents divorced when I was the same age as your youngest. Within 30 minutes of my mum saying she was leaving (she met someone else) they wanted to know who I would live with and said who ever I picked got the house. I wasn't equipped to make that decision and picked my dad because (a) it had been his house and (b) I didn't want him to be alone. It was a bad decision.
My advice would be let them take their time. Don't make then commit. Let them know they're equally welcome at either house and give it time to see what works. As they grow, leave school etc things might change. Try not to take it personally if they pick the other parent.