My aunt wants my diamond

My grandma passed away a few years ago. My grandpa also passed away just recently. Before he went, he gave my now fiancé the original diamond from my grandmother's engagement ring to propose to me. It made the ring so beyond special to me that I cried. Well, since he recently passed my family had to go through all of his belongings, including the rest of my grandmas engagement ring which had been upgraded on their 25th anniversary. So the diamond I now have is one of two smaller diamonds beside a larger one in the center. One aunt is getting the middle diamond, and my other aunt wants to make the smaller diamonds on the side into earrings for herself. But problem... One of those diamonds is on my finger. She has a lot of money and she told me she would buy me a bigger one. She said I should think about it. But I don't want a bigger one. I want the one my grandpa wanted me to have. But I feel guilty, and I don't know what would be the right thing to do.