I'm not clear if you actually have POA documents in your hands, (or indeed if your brother is actually using it)? If not, priority is to get hold of the solicitor who arranged it (I'm assuming a solicitor did it), and get yourself a ceritfied copy. They are not going to notify your brother, and you have
every right to have these.
I think any complaint about your brother's conduct in relation to your mum's affairs should be addressed to OPG, I can't see what a solIcitor would do about it.
Please don't discuss these things with your mum. I know you feel you should, but she is beyond logical thinking, and it is just muddying the waters. You
know what your mum
needs - we are way beyond what she
wants now.
It may be worth trying to get another SS assessment. Explain that your mother can't take phone calls (her phone is blocked) insist that she is visited and make sure that you are there when she is assessed. On the day, don't wash her, dress her etc. - SS need to see her normal life. That said, as she would be self-funding, they may be very reluctant - you will need to use words like "vulnerable adult" and "duty of care". If all else fails you could call anonymously.
Failing that, use your POA to organise a carer (maybe just a couple of hours to start with), and make sure you are there to let them in etc.
As
@MartinWL has pointed out, - if your brother is too ill, dies, or is abducted.
you have to be able to pick up the reins , which means you have to know what is going on.
I mainly deal with Mum's finances, as she lives with me. My sister is registered on a current account and a B/S account - if I die tomorrow she can access these monies immediately. She also has details of all the other accounts that Mum has (passwords, acc. numbers etc.), so she could register her POA to access these, if required.