What your family is doing is cleaning some of their guilt about your grandma, so let them clean their sins while they can. If that make them feel better, so be it.
Your position is more or less, "saner" than what they have. So you could let her go so much easily when the due time will come.
I had a similar situation with my grandma, the alzheimer hit hard the whole family and she didn't even know who I was and neither any member of my family too, but some times, that little moments of lucidity brought happiness to the whole crew, and she was comfortable with that, so I had to made peace with myself that I had lost my grandma a long time ago (before she past away), because she wasn't there anymore, just her body (this is not a rationalization) and some incoherences of her brain, really I can tell you this disease is a fucker of souls.
So let her daughters/sons do what they can, while they can. The issue is you, the thing I can say to you is: You just leave her when she has to go, with a broad smile in your face, and remember the good old days of grandma.
I can tell you she raised me 'till I had 12 years old, and she was like my second mother, a very sweet old lady... Hell, she was my second mother, do I miss her now?? hell Yes!, but I let her go because is the rule. She past away when she was 87, 2 years ago.
The only thing you can do is witnessing her departure, and from the bottom of my hearth I say: Is a pleasurable moment seeing a person go leaving the body pain behind, and remember it with all your love and how they took care of you, and that you are a companion in her last days.
Stay strong brother.