@RANGIEBABY When I read your post above, it resonated with me and the part that hit me was, “and [she] needs to keep her family together.” That is one potential outcome of this situation (and possibly the one you see as the best outcome), but it is not the only outcome. Candidly, it may not even be the best outcome for your son or the children.
It sounds like your son is unhappy and he has said that the marriage is over if she doesn’t change her behavior. If she is mentally ill, no amount of “trying” is going to make her or the situation better. Mental illness is a medical situation.
This situation could go in any number of directions and I think it is important for your son to decide, for himself and the children, what is the healthiest long-term outcome for them and to determine how he can best navigate them from here to there. I don’t know if he adopted her kids from the previous relationship, but it sounds like he made need therapy to clarify the situation for himself and become clear on the best possible outcome in his mind. Then he may need a lawyer to put some of the pieces in place to see that outcome to fruition.
Unfortunately, he is stuck being the adult in the situation and he will be helped in his decisions in the coming months if he is clear in his convictions. For example, an attorney might advise him to document some of the behaviors he is seeing particularly if they put any of the children (or him) at risk or even if the wife puts herself at risk. He will need to have a plan and to be thorough in its implementation and advice from professionals will only help at this point.
She may choose not to seek help, but he would be well-advised to do so.