Wow, I can understand your situation. We've been through something similar on a very small scale here. First of all, I do think you are allowed to get involved – up to a certain degree. It concerns you as well. I also get involved when my husband considers buying his daughter from his first marriage an iPhone now and then. His spending habits also affect my life and that of our children together. Otherwise, regarding the case: Why the hell are the two older children living in the house rent-free? Whether they were my children or my partner’s, a reasonable rent would be mandatory, especially if both earn money (they do/did, since they no longer have maintenance claims). It’s more difficult with the 17-year-old. I would talk to him about whether he wants the maintenance and then pays a small rent to dad/mom. That’s how we handled it with my husband’s oldest son. But since we knew the mother would get nasty and ask for an impossible rent, the money still goes directly to the mother until the boy moves out. What I would do in his place: Whoever lives in my housing unit pays rent, no ifs and buts. A family discount can be taken into account, of course. I can’t decide about the woman’s housing unit, that’s something she has to arrange. I would offer the youngest to move into my apartment to get him out of the situation and off the street. That would also end the maintenance payments to the ex. Then off to the lawyer to explain the situation precisely and clarify legal options. Sounds like there’s not much that can be done. Then as a last option, sell my share. Whether the children complain or not wouldn’t matter to me. They can move out or agree on rent with the new owner – they are old enough for that. The sale would hurt, but that way you can make a clean break. Otherwise, you’re stuck again with the ex and have to pay for repairs because that stupid nut doesn’t contribute. Oh, and I would have rolled my eyes, too, if the older one was whining about maintenance. Our 18-year-old understands how that works as well.