Oh man!!! Okay, I have been there. I can give you my experience anyway.
We didn't have a coordinated effort when we did it...I did it. I just sat my then 10.5 year old daughter down and told her that mamma and dada were no longer going to be living together and that we love you very much. She melted into a puddle of tears and I just held her. As the days progressed she asked lots of questions and we started making changes in the living situation. She just wanted love...she wanted some information, and that came as things happened.
Remember you are dealing with an insane person, and you have to be the one in the drivers seat, if he will agree to details, then great. If not, be prepared to be the one who has to bare the brunt of this storm. Your kids will survive. Give it to them in bite sized chunks. We are sererating my love, which means that mama and dada are not going to be staying in the same house. Stop it there. Let it sink in, give them love, reassure them that they will be ok. Show calm and love, that is all you can do. Here for you ok.