Hello! I’m in a very similar situation as you with my Mum. I have distanced myself because she will still find a way to drink if someone is living with her or not. I think it’s important to think of yourself because your Mum makes a sober decision to drink when she could think of you and your family.
My mum is currently in hospital after I called 999 as she told me she was going to kill herself. Since speaking to her over the phone she has no remorse or idea what she has said to me which makes me so mad!
Just be there for her when you need her and take care of your Dad.