Hi Guy
I think we could go round and round in circles about who own's what gravestone, but as far as I am concerned my ancestors bought and paid for the grave stone or plot,and we have both, one side has a plot and the otherside of the family has grave stones, and I think it is my duty as next of kin to keep it clean and neat for the next generation of my family. If it means removing moss etc so be it, as there are plenty of other things it can spread itself over.
ricky