I talk about it very openly w/my 9 and 15 yo girls now that we are divorced, and when we were married. The thing is, you have to advocate for them and make them #1. Addicts hate that.
I put both of my girls into counseling with a counselor who specializes in helping families who deal with addiction. She also happens to have a daughter the same age as mine, so that certainly helps too.
I think it's very very important not to brush this under the rug. Talk to your kids about it. Talk to their counselor at school and their teacher. Let them ask questions as they will have many. If you don't know the answers, be honest. Above all else, be very honest.
What I found is that there was no hiding it, and in trying to do so I was making my children very angry b/c they knew there were problems in the home and needed to talk about those, and to know they are not at fault, ever. I also agree, you will have to make sure that he never drives your child under the influence. Be on your toes all the time. I never ever thought my X would do that. Surprise, he did, a few times. I put a stop to that right away.
I am sorry you are dealing with all of this.