Being on the other side of your discussion, I was once a drunk homeless ex that thought the same scenario was acceptable. We have twin boys that are seven.
My ex told me straight out that I was never ever staying at her house under no circumstances. We are best of friends, we speak everyday on every topic, but are never get back together.
And, We still have a problem that I live in a half-way house and can not have the boys stay with me. I have been sober for about six months this time and feel great, but understand that I will not be staying with the boys over night until I get my own place.
Tell the ex you understand, but sorry. The girls will slowly grow the recovery with Dad and will learn that for now Daddy is not staying with them.....It might also give him a kick in the pants to start a program of recovery.
Good luck!..
PS: This is a program of honesty and tough love. It will be better if you are honest now and nip this and other things in the bud.