I think when someone has dementia, or clear signs that they are not competant a court orders a POA. I might just go ahead and and take him to notary, as it is legal. If he doesn't know who is or have any idea where he and what he is signing, then I would think the Notary would halt?. Then I would ask an attorney to get POA. You can even get a temporary POA (at least in California). People get them all the time, especially if they are undergoing life threatening surgeries or illnesses. When they are well and cometant, they have the POA voided.
kathypet, I am so sorry you are going through this. By best goes out to you and your family.
“sometimes you have to bite your upper lip and put sunglasses on”….Bob Dylan