My mum and her brother's partner have been managing my uncle's affairs since he was diagnosed with Parkinson disease. What are their rights?

I think you need to do whatever you can to get some answers. If your uncle is upset, then he may need to be upset in order for him to get better care. Also, unless he is upset long-term so that he doesn't eat, he may say you're ruining his health. but I doubt if that really will happen. Being upset alone won't kill you! If you are unable to get some of these things straightened out, on the other hand, he may end up in a totally untenable situation.

I also have one question. Further on, you say that your mum is in SA? What is SA? I live in the U.S. and don't think I've ever heard of it. Thank you!

Thanks so much for your response I reside in Ireland my mum is in SA. Yes an attorney is the solution but we also don’t want to upset my uncle too as this affect his health . He also doesn’t want to fight . Sorry but I don’t know much about his assets and and who is in control of this . I’m assuming it’s that partner but he has no bank account . My mum knows who his lawyer is as he was a customer of my late dad so I’m not sure what she should do . He has mentioned that everything will be left to her but we don’t know what his assets are and have no paperwork to confirm the same

YOU NEED AN ATTORNEY.
This is a total and complete mess.
I certainly have no idea of what is happening.
It sounds as though your Uncle has a female partner who has tired of care of him, and because she is merely a partner she has walked away. Do I have that right?

You use "mum" and I am wondering where you reside, for if you are in the UK the rules and regulations and the protections may be a good deal different than they are in the USA. In this situation in the USA everyone may well be going down with the ship.

What is going to happen here entirely depends upon who is LEGALLY designated as WHAT and it sounds like you don't know the answer to that?
Hence an attorney is needed.
Questions here you need to know ASAP:
WHAT are Uncle's assets ?
WHERE are Uncle's assets?
WHO has control of Uncle's assets?
WHO is POA for Uncle?
Is Uncle competent enough to appoint his sister as his POA or you, his neice, and are you legally able to do all that a POA must do to find his assets, keep track of everything, place him in care and protect him?

As I said, this is a tangle. And it is going to take a whole lot of sorting out. I am hoping this woman, the partner who has walked away has not walked away with assets they may have comingled, because if so Uncle in not only deserted, but he is broke.

I surely do wish you luck and I surely do hope you keep us informed.

Find an attorney now.
If you ARE in the UK and you have a Social Services System and National Health that is a good deal better than ours you may be in luck. Otherwise I shudder for this situation.

You Need to tell the partner to hire Help as mom Is Burnt Out and encourage Mom to take a vacation .

Ai much?