Calluna,

nickle730 has explained it really well. You can't do it unless she agrees or she gets declared mentally incompetent. From what you have said, I think it would be highly unlikely that she would be declared mentally incompetent. She may be making silly choices but at the end of the day they are hers to make. While I think it is lovely that you want to help your mother, and in your shoes I would be tearing my hair out and wanting to do something too, I'm not sure it's up to you to "fix" your mother. Your mother and brother are both legally adults. They are old enough to live off their own decisions. If she had minor children in her care there's other things you could do but they could get very ugly and you might end up destroying your relationship with your mother.

I can't imagine she will take kindly if you try and have her mentally assessed without her permission? I think you should try talking to her. Suggest she give the majority of money to you for safekeeping perhaps? Good luck honey. what a tough position to be in. The other thing I wanted to say though is that I have learnt through recent events in my own family that your energy should be spent on your family- your partner and kids. Looking after your mum sounds like it could be a full time job? Do you really want to take energy away from your family? I say that though through very jaded eyes.