Hi LTPF
The elders need to be careful they do not pressure people into signing the advance decision. The law here in the UK says that the advance decision is only valid if you have filled it in of your own accord/voluntarily without undue influence or pressure from anyone.
The only thing the elders can say is that there are advance decisions available within the KH. If they pressure people by going up to them directly asking if they have filled them in or asking for a copy, this may deem the document invalid by the medical profession.
Note: I am surprised they still hand them out in some places. They don't do that here. You have to go to the book room to collect one. This is likely due to the laws around advance decisions.