Yes we all do try to look out for each other around here.
I have read through stuff and I have some thoughts, please bear with me...
I am concerned that your S has stopped calling you mom and dad. While I know people who allow their children to call them by name, personally, I don't feel it is appropriate.
Does it bother you when you S calls you by your name (which you said he does when he is upset with you)?
Personally, I would gently remind him that to him, you are Mom. And that is what he is to call you. And don't respond when he calls you something different. It is a boundary of sorts and it is a way of establishing the roles in the family of a heirarchy of sorts as well as a term of endearment.
As far as what he calls your H, unfortunately, that is between them.
Additionally, while I understand you wanting to go to counseling in order to help your S, and ideally it would be wonderful if both of his parents went, it isn't something that you can push on your H. That doesn't mean that you shouldn't go yourself.
Often when we try to get them to see what the children are going through, even though our motives might be pure, it is seen by our S as a way to manipulate them into changing their minds.
Regarding your M, do you want to reconcile it or do you simply want an amicable D?
Probably a hard question to answer right now, especially considering your recent revelations regarding your H's family.
An important one nevertheless...
Regarding him and his family...
I was overwhelmed by the way you describe the chaos and the craziness. It is a hard thing to live with but not impossible as you have been doing it for many years now.
How has that craziness affected you? Really affected you?
I can tell you that simply leaving it isn't going to make it go away. It will still be there and it will still have the opportunity to take it's toll until you gain some understanding of the dynamics and decide how you are going to react to those dynamics.
Are the relationships you have with these people really serving you or are they hurting you?
Oh I could go on and on but I think that is a good enough place to start for now...
"Acceptance doesn't mean resignation. It means understanding that something is what it is and there's got to be a way through it."--Michael J. Fox