I had a massive row with my younger sister who wanted to see my T some years ago. It felt for me (amongst other things) like she was violating my privacy and not respecting my boundaries. This might be due to our shared history.

But apart from my personal reservations: My T kept saying that she would never consider treating any close friend/partner/relative of any existing and/or former client of hers. She would refer them on to colleagues who work in the same practice or elsewhere, if they wished so

I was quite intrigued by the fact that she even said "former" clients. Her answer was, that in her opinion, former clients of hers should always have the option to come back to her, should they feel they need to. This might not longer be an option, if she started to treat friends, siblings relatives of those former clients.
Which I found very re-assuring and comforting, just knowing that my T is still out there and available, even though our actual work has been finished.

ETA:
Schizoid_1 - how do YOU feel about this? It's great that your brother doesnt mind, but maybe you do?