I went back and looked for my original field notes that I took when I inventoried the Myrtle Hill Cemetery; that was probably about 1990. Needless to say, I did not find them, so I'm having to depend on what I transcribed to the burial index card. I note that Isaiah Barnett is apparently buried in in the Barnett Family plot in Myrtle Hilland I suspect that the proximity of graves is how I concluded that the two were brothers. That seems like a lot of information to be on a tombstone, but sometimes there is that much.
There is an old Floyd County (Ga) History, printed in the 1930's, and it has a good deal of WBTS info in it. Perhaps some of your contacts have access to it; I do not know the name of the author, or even the exact title, but I disticctly remember using it. It has a listing of the graves in the Confederate section of Myrtle Hill, but not of the regular Myrtle Hill burials. I live in S.C., and the nearest libraries that have the history of which I am aware are 2 1/2 hours away. It may have had some data on Barnett. I simply don't recall. I will try to remember to look through the history the next time I have access, but that may be a good while.
Unless one has been published recently, there is no cemetery survey for Floyd County. Perhaps you could post a reqeust on the Georgia Board to have someone verify the information on the Barrett tombstones.
Good luck on your search.