If they just recently purchased the property then they should have an abstract of title. That will tell you the former property owners. If for some reason they don't have a copy of the abstract they should be able to get a copy from the abstract company, since they are the ones who paid for it. Since it is rural, an enumeration district will tell you about nothing. You or they could go to the county and trace the title chain through the Grantor/Grantee indexes. The Grantor/Grantee Indexes probably go back to the Revolution, if not before.
As far as previous cemetery listings, Albany County Cemeteries, by Col. William V. Hannay likely has the cemetery recorded. I can't remember the time period exactly, but he probably did the transcript 60-70 years ago when you could read the stones better.