Praise be to Allaah.
These people were originally buried in land for the dead (a graveyard), and they own it by virtue of being buried there. It is not permissible to disturb them, whether by digging up the remains, walking over the graves or any other form of disrespect. You should put up a fence around the graves so that they will not be subjected to any disrespect, and so as to preserve their dignity, because the sanctity of the dead among the Muslims is like the sanctity of the living. May Allaah bless our Prophet Muhammad and his family and companions.