Confusing the baby


So my older sister J is a single mom and is currently living (rent free) with our oldest sister M and her fiancé. M is a good person... to a fault. She always puts everyone else’s needs above her own. To the point where it has let to depression and anxiety. J is extremely selfish. She always puts her wants first. She’s ruined relationships lovers and friends. The main thing that really gets me has to do with her 1 year old child. First off she cheated on a great guy to get with this druggie fuck boy (her words) who knocked her up, claimed he was going to be there for her and the baby “so she wouldn’t kill his child” (his words) and then promptly went baby to his ex. She had her child “because she was 34 and if she wasn’t gonna have a baby now then when?” Moved back in with her sister and now pawns her child off on her family so she can still go out and party. Then she gets mad that her baby gets more upset when M leaves then when J does. She’s constantly putting M down with phrases Like “I’m her mother, I know better than you!” Wtf? And M really feels bad about it. She doesn’t want to be more important in this child’s eyes than her own mother. But she’s more than happy to spend time with her niece and care for her. It’s really stressing her out.

Example: my SO had invited her and her Fiancé over for dinner and drinks a few nights ago and she spent a good hour worrying and feeling guilty that she had to leave J alone with HER OWN CHILD for a few hours.

She asks for my opinion on what can be done and honestly shy of J moving out I don’t see this situation resolving itself. The child’s going to start talking soon, and i can see J losing it when her child calls M mommy.