What right has anyone to go against those wishes and install cameras anyway? - without at least some form of independent oversight my opinion would be that nobody has the right to do so!

It may depend on the reason for those wishes.

A daughter may suspect that her mother is being ill treated but the mother is absolutely sure that all cameras are satanic devices which will steal her soul while she sleeps.

If and when dementia sets in totally irrational thoughts can appear and sometimes elderly people do need protection against themselves much as children do.

With my mother I had to decide at one point whether or not she had got to the stage for me to give permission for her to receive help if she had an accident during the night rather than leaving her to sort herself out.