May I make a few suggestions?If this were my family I would research G.A., see if you can either prove or "disprove" him.That middle initial may stand for Andrew,hence a possible mistake in someone's memory on his full and correct name, it does happen from time to time.(^_^)
Unfortunately the 1880 census does not ask information regarding land ownership.If G.A. died in 1885 and owned land, I would be looking for probate, land and guardianship records for the minor children.The court would appoint a guardian to report back on the sale of any of that estate, to protect the interests of the minor children until they reach adulthood.When land is sold, all heirs, or their guardian (in their name) will have to sign off to give clear title to the buyer.
You say you have been told the names of the parents of John, how about his death certificate?Do you know when and where he died?Did he live long enough to obtain a Soc Sec card?If so, you can obtain a copy of the application he filled out, it should show the names of his parents, his residence at the time of application and other data, too.