RED FLAG ALERT!!!! Your AW sounds like she's trying to be slick. So glad you got wind of what they were planning. Be proactive in this. Go get a consultation with an attorney - even if you have to pay for it. (I had to pay $400 for about an hour and a half with the one I saw, and I never filed for divorce or separation, but I can promise you the info and advice he gave me was well worth it)
Your child needs the most stable and consistent life possible. That does not mean uprooting him and moving to State C with alcoholic mom and her enabling family. I know why you did what you did when you did it, but it's not a long-term plan, nor did you ever intend for it to be. Good for you for nipping this in the bud.