It's a sad situation. Your son has quite a dilemma on his hands. He'll have to work it out as best he can. It is tempting for you to believe that you know best how to handle this. Your ideas may even be good ideas. The problem is that none of this is for you to decide. I think you need to let go.

Your son got involved with a very unbalanced woman. (She has 3 kids by 3 different men. So she bounces from relationship to relationship.). That may suggest that he has some psychological issues of his own. For him to make good decisions, he needs to be mentally healthy. He needs to mature, himself. The surest way for you to sabotage that is for you to be over-involved in planning what your son does.

If a lot of your time is spent trying to figure out solutions for your son, then your life is out of balance. You need to pursue your own adult relationships and your own interests. Of course, grandchildren are one of those interests, the role of grandparents is not to arbitrate the relationships between their children and grandchildren. A grandparent's role has to be more passive. That may be hard for you to accept, if you are a natural problem-solver. It sounds like you are.

Having an unruly child behaving badly in your home is a situation you have a right to exert some control over - in your home. What transpires between your son and those boys away from you is something you need to not make a focus of your attention. Naturally, you want your son to be happy. But he's a big boy, now and his life is for him to figure out. He's going to struggle and make mistakes . . . maybe some big ones. Maybe he's in the habit of confiding everything in you. If you are his main confidant, he needs to find a new significant other. Sometimes it is appropriate to act a bit detached from your adult child's doings. He needs to see that you have your own life, relationships and interests. One way to promote your son being happy is for you to role model living a fulfilled and satisfying life. Time you spend talking to lawyers about your son's options would be better spent doing your own thing, whatever that may be. Obviously, you are educated and have built a successful life. Undoubtedly, you have interests. Pursue them with gusto. Shift your focus.

You asked for suggestions on how to convince your son to do what you think is best. Even if that were achievable (which I doubt), that is not what your goal should be. Even if you have the wisest ideas about resolving this difficult situation, it's not your problem to solve. Yes, the older boy misbehaving in your home does create a problem for you. You have a right to address that. That's more than enough of a challenge for you, without you also trying to figure out what your son should do.