When our mother died, she had no plot. So she was cremated and placed in the plot with her parents and sister. Six years later, when our father died, my sister and I dug up my mother, under cemetery supervision, and placed her in her own grave, with our father. We dug and buried them both. One of the first acts of my sister, as co-Trustee of our father’s estate, was to suggest that we use estate funds to purchase a plot for the two of them. Agreed.
Turned out that our mother couldn’t have stayed with her parents and sister indefinitely. There were noises from somewhere that to do otherwise could cause an influx of urns from diverse sorts, ending up in the grave of the parents and sister. So our mother stayed in there for six years, specifically without a marker, and with the expectation that she would be moved.
Didn’t knew who had made the call. Turns out it one of our mother’s brothers, who presumably was the trustee of the estate when the plot was first purchased, at the time of the death of our mother’s mother. That may have been fine at that time, but as years go by, the rights in relation to a the control of a grave appear to either stay within the original purchaser’s estate or become the rights of the beneficiaries of that estate. If, twenty or thirty years later, one wants to place a family member in that grave, one would appear to need to obtain consent of what could be a scattered group of beneficiaries, if the estate has been wound up. The rights to a grave are not regarded as creating an interest in land, but rather more like an perpetual easement–a right to use and control the use of that particular plot, subject to the regulations of a particular cemetery.
Since cremation appears to be more common, there are many graves where there would be room for urns. A coffin goes down six feet, and one can generally place up to three urns above a coffin, three feet down or so.
Something perhaps requiring greater specificity in wills, or some sort of default legislation.