Need help to understand and help my partner
It is reassuring to think other people will be around your partner's mum if she goes to live with her. I'm just not sure your partner can be trusted to tell anyone of her problems with her mental health & alcohol while she can hide it, so I would be considering having a quiet word with the brothers, so they can be prepared if problems do arise.
& I am wondering, about you, & what all this means for your relationship with your partner. Mentally/emotionally how are you travelling?
I'm hoping you find some time to care for yourself.