How many people can their be in a Joint account, want to set up a joint account with my mother who has now moved into a care home but also include my sister.
Two.
You need much better functionality and legalities than a joint account.
That’s not what joint accounts are for.
This may be helpful. Some banks do offer this
Should of said there may be better/other options you should consider too such as power of attorney and third party mandate access etc
There are other things to discuss here but this is the answer to your question. And will be the same answer with any other bank.