My dad did the very same thing when my grandmother died--I found out later that he actually took a load of my grandmother's treasures to the dump. That was years ago. I think it's sad that my father doesn't appreciate the connection between generations, and that's his loss. It's the same with your sister--how sad for her that she doesn't see the importance of connections.
It was easier for me when I looked at how sad it was for my father to be so lacking in compassion, rather than to feel sorry for myself--because no matter what, I know my grandmother loved me--and that's the most important thing anyway.
This same grandmother once told me, "The answer is already No if you don't ask." She was trying to tell me to go ahead and ask, because I was like you and wouldn't ask. I'm better now, but not nearly as open about it as my sister. :)