Hi, I’m so sorry you are going through this. This is just my opinion but I think you really need to talk to someone in order to protect your little brother. It sounds like you love him so much and as hard as it can be to speak out, sometimes that can be the best thing in the long run. Maybe having other people involved will help her see the light? It must be so difficult for you seeing all this and not knowing what to do. Is there someone you could speak to about protecting your brother? Maybe a teacher you trust?
I know from personal experience my dad won’t ever admit taking drugs despite him doing it for over 20 years and me being 30 now. He pretends like it’s nonsense even though it’s ridiculously obvious. I think a big part of it is that he’s ashamed to admit to me, his daughter, that he has a problem as he doesn’t want to disappoint me. Perhaps this is the same for your mum?
I really hope things get better x