Croping up regularly in various postings … numerous guides around ( Including elsewhere on this site ).
The following is the closest you’ll get to a BIBLE on this difficult area … 46 pages in .pdf format :
A guide for family, friends and other unpaid carers.
Helping people who are unable to make some decisions for themselves.
( MODS … if it proves to be useful , time for a STICKY ??? … a stand alone one , be lost in that new CUK one. ))