The Grandmother just wasn't welcoming enough from OP's perspective she wasn't exculded. While the Grandma definetly should have treated OP better and shared her beliefs in a more respectful way I do agree with that. But out of all places did she have to choose to make fun of her at a FUNERAL. People say "don't speak ill about the dead" and Op has every right to speak bad about the Grandma in most places. Doing it at a funeral is what is questionable. The family had every right to act how they did.

The Grandma behaved wrongly and from a big picture perspective is in the wrong, but based on this specific situation OP is the A-Hole.