Gaslighting?

tell them you have a safeguarding concern.
sometimes you have to use the jargon to get any action.
glad she's got you to look out for her. so many have no one.
good luck.

you should consider reporting the situation to social services, elderly care, as it looks as if a vulnerable person is being abused.
please don't wait until an ambulance is needed.

I would be very worried about the effect your brother is having on your mother, especially as she is more vulnerable because of her age. Could this be classed as elderly abuse? Please keep a watchful eye on the situation. Her doctor could be a source of help.

I think you’ve hit the nail on the head Jaxjacky. She has to be careful what she says around him and I think it confuses her. She has just callee me to say her purse has disappeared. Yesterday it was the phone broken and boiler not working properly, day before her bag disappeared. All since my brother arrived.

Could this tie in with your other thread ‘90 year old Mum getting forgetful’ SecondhandRose?
Maybe your mother is not so forgetful, just upset with this situation.

Perhaps he wants her to need him to be there, therefore making himself indispensable, as Elizabeth 27 said it is all tied in to his own problems, make your mother aware of your concerns and say if she feels as if this is happening to let to you know perhaps you can have a a password or phrase that she can use so that if she needs to phone you and he is there she can just say the phrase. make sure you are "popping in" regularly so that you keep and eye on the situation also does your brother have a Social Worker make them aware of your concerns so that he can be re-allocated a place more quickly as it is putting your mother in a vulnerable situation.

What are his mental health issues? Maybe the ‘gaslighting’ is not intentional.