How do you feel about me paying my sister to make up a memory of my grandfather for his funeral since I don't have any of my own?
Could you tell me what you're paying her with?
Money and a promise that I won't be her enemy anymore.
It's good that you want to be respectful of the memory of your grandfather, but I think it would be best to just be honest. If you don't have any memories of your grandfather to share at his funeral, that's fine and I'm sure people will understand. Your family will just appreciate you showing your support by being there regardless of if you have a story to share or not.
This is exactly how I expect human nature to work.
Well I hope you decide to take my advice and tell the truth to your family. I promise they won't be upset at you just because you don't have a memory to share. As long as you show up and support your family through this difficult time, people will understand.