I'm not going to help my dad repair the damage from when my grandpa's house burned down
How could you not want to help out after such a tragedy?
My dad mentioned about the fire but there was no sign of sorrow on his face.
This sounds like a really large issue that he is having. Maybe you should think about helping your family in a crisis? It's polite to do what you can to help people when they are having a rough time of it.
He only told me about it. I don't owe them anything.
He may have mentioned it on the assumption that you would offer to help him with the repairs. Instead of making a bad situation worse, you should ask outright if help is needed.