Honestly, it sounds like they're mad at you because they CAN be mad at you. You're still the safe one.
They have finally agreed that's it ok for me to date but absolutely not to get remarried.
I winced so badly when I read this sentence. You're an adult too! I admit it's kind of icky to think of your dad dating and GASP doing the horizontal polka, but it doesn't mean you ban him from marrying someone else. You don't need their permission.
Have you thought that maybe they harbored a secret hope that by pressing for divorce, their mother would change her ways and stop drinking? And then the both of you would get back together? Having you move on ends that particular fantasy, which means that the grief has come on full force. And since you are the Dad, you still have a role in protecting them from those bad feelings. How do you stop those bad feelings? Stop dating!
Unfortunately, it doesn't work that way. I think the dating/no marrying statement is their attempt at negotiation, to keep at bay the confirmation that it is truly over between you two. Your XAF drank when you were married to her, she drank when you divorced her, and she'll continue to drink no matter what you do. We don't know what her bottom is, but it's best for ALL of you to detach before she drags you to a place of no return.
For the record I encourage them to have a relationship with their mother.
IMHO, I wouldn't try to encourage them to talk to their mom. I wouldn't discourage it, but I wouldn't pull out the pom poms either. You just ended it with her, why should they have to continue to bear the burden? So you can go off and date without guilt? When people encouraged me to have a relationship with my abuser, I hated it. All it did was make me feel guilty for cutting off the connection in the first place.
Argh, you are not in an easy place. I do hope your children heal.