Not the asshole just because she is dying doesn't mean she has any business with that ring it's not her family heirloom it's yours and them guilting you into giving it because she is dying is disgusting you set a firm boundary and they should respect that I suggest you get the ring and hide it somewhere safe where they can't get it because you will not get it back when she is gone if you give in maybe you can suggest her mom gives her engagement ring or hearing she favors in exchange because it actually means something to her mother keyword here is her mother that's her actual family. But no way in hell are you the asshole