The standard of euthinasia in the US for old people is to both starve and dehydrate them to death, and then what they do is give the family a little finger-sized sponge to keep the mouth moist because it's super painful when that dries out and so the family can feel like they're doing something nice. In reality, the patient is on a crazy pill cocktail to try to numb the pain, keep them in a coma-like state, and stop the natural spasms that accompany death from dehydration. It's a terrible way to go, but it funds the medical industry and gets an old person dead sooner than later without drawing it out and with an official excuse for the family so they don't have to feel bad about letting "natural causes" or whatever do the dirty deed.
I had one grandfather who straight up refused to eat once he decided he was done and didn't want to drag things out. He out and gone within a week, but he had wanted to die, and the last time I spoke with him that's what we talked about. He said he wished more people would respect him enough to let him die in dignity at his point of choosing. So talk to them now if that's what you're worried about. You might find yourself some day having to make a decision without them having any say in the matter.