No discussion could take place as my cousin's father died about 20 years ago. It would appear that because her father was the last of his family living at home with my grandparents, he automatically got their house and farm and His family now assume ownership of this grave.
I've never heard of parents leaving a cemetery burial plot to their offspring. I know my own parents did not mention their grave in their will so I would assume all of my siblings have equal right to it.
I am reluctant to get into a discussion with my cousin until I can establish the legalities of the situation.