Cemetery Lots belong to the person or persons who bought the lot. If those people are deceased, the lot belongs to their estate. The executor or a majority of the closest surviving heirs can then allocate space in the lot.
A better solution is to have the persons who own the lot file a letter with the town clerk listing all the people that are eligible (or not eligible) to use the lot. If the original owner is deceased, the person filing the letter should be the executor of the estate or the majority of the closest living heirs.