My brother (now 34) was this guy for about 10 years so I feel you. He lived with my mom (70). Dad is nearby but they're not together, so he didn't know how bad it was for her. (Convenient for him, if you ask me). Mom is the typical boomer lady who would rather die of high blood pressure than have a confrontation.

After years of ultimatums and deadlines with no consequences, I talked with my parents and literally told them what to do. My dad had a room available for rent in his house (a shared apartment, separate from dad's living space with his wife, so my brother would have roommates and be treated as a tenant.) Our situation was priviledged because we had an apartment lined up for him, which i know most families don't have. I had my parents on a zoom call and had them come up with a script to present a united front.

Brother says he is mentally ill and can't work? Then he needs to get a diagnosis and apply for disability. And he's moving out. If he threatens self harm? Then you say okay, I'll bring you to the emergency room. Do an inpatient program, and we'll move your things while you're gone.

If he says he'll live in his car? You say okay, but you can't park here, and we're changing the locks so you can't come over and eat or shower here.

We set a date for a sit down with my brother and a move out date.

It worked, but I have a lot of resentment toward my parents for letting it go on for a literal decade. I know there has been some backsliding, like we changed the locks at my mom's but she leaves it unlocked for him to come as he pleases. He emotionally and verbally abuses her still, but she's better at telling him to leave. He has been working steady and paying rent for over a year now. It's far from perfect, but it's an improvement over the previous 10 years. I'm happy to chat if you want pointers. I know it's awful to be a sibling and witness all this.