Praise be to Allah.
We put this question to our Shaykh, ‘Abd ar-Rahman al-Barrak (may Allah preserve him), and he replied:
Rather if this land belongs to them and they have designated it exclusively for burying their dead, then they have the right to prevent anyone else from being buried there.
But if it is public land that is not owned by them, they do not have the right to prevent that.
And Allah knows best.