Given the complexity of the situation, I most strongly suggest getting
the fully considered, case specific advice of your own lawyer.
Among other things, a Power of Attorney being granted to somebody
does not in itself place the donor under a legal disability.
Rather, it works in the other direction. It allows somebody to act on behalf of the donor
when the donor is without capacity (such as when ill, or imprisoned, institutionalised,
or simply, say, overseas).
The bit to understand is that a Power of Attorney does not itself create that incapacity.
So, a person can be, say, out of hospital, and doing their normal, everyday thing,
on their own account, even if the Power is still in place.
All of which makes it hard to give you a simple answer.
You're on the right track - in that somebody will indeed need to be the Respondent
(the person on the legal "receiving end") in what you're trying to do.
But who that should be in this case.... and whether it can (or should) be the principal,
or their Power of Attorney holder, and whether or not it can (or should) be same person for business and personal aspects...
those are questions for a properly instructed lawyer who can get across all the facts and circumstances.