I agree with Babyjane.
This woman appears to be after the money!
When does Power of Attorney kick in? Maybe change the locks on your Mum's house [which we did for mine, long story short] and have a key-pad on a need to know basis? In recent weeks we've changed that number too as she was giving it out to all and sundry and we felt that her security had again been compromised [longer story short].
I would ring your Mum's GP and ask for advice, he may be able to let you know what did the Hospital advise B4 her discharge? Certainly it's time that he/she knows the full picture in case your Mum becomes even more confused. I would ring the Ward Sister and ask who spoke to your Mum so that you can have a chat with her/him? Time that a Social Worker was involved.
A Solicitor could be instructed to put a restraining order on your brother/s. Do you or your Mum have a family Solicitor? Despite the issue of a newspaper delivery, it could be stressed that either they visit when the Social Worker or yourself are there ……. it would need to be worded so that your brother/s didn't turn it so that you are forbidding access which is really what you need to do
Well done the Niece!
maybe once this brother has thought over what has been said he might buck his ideas up!