My MIL has let BIL back to live with her more times than was good for anyone.
He, however, is a feckless sponger, who works until he falls out with people, refuses to ever have a permanent job, preferring short term contracts, and who drinks too much. He becomes verbally abusive and aggressive when drunk, sometimes leading to physical aggression too.
He came back to live with her when we moved to Australia. There was a massive fight between him and DH - we left that night to come to our unfinished house. We had an AVO out on him (same as a restraining order). But he lived with his mother - up until the situation became so untenable that she was pretty much begging the neighbours to call the police on him (she felt she couldn't) to get him arrested and out of her house. She lost weight, she aged, she looked ill while he lived with her - but she didn't feel able to tell him to get lost.
He went away for a while - but then he came back. Almost immediately she started to become unwell, but then he broke his good behaviour bond and ended up in actual jail. She won't have him back again now.
However, she STILL makes excuses for him and blames me for "breaking up her family" because I won't have the sorry excuse for a human in my home (He called me a lot of fucking names in front of my then 3yo and only left when I pulled my phone out and threatened to call the police). He's in jail again at the moment - another break of AVO/good behaviour bond.
This is an EXTREME example - I know that - but my MIL put herself into this situation by not standing up for her own rights to a peaceful life, and allowing this sponging manipulative "manchild" back into her home, rather than turn him away.
DH would love to be a manchild - but I don't let him, as far as I'm able. He still tries it on though.