There were a total of 10 Shellnutt, Shellnut, Shelnutt, Shelnut of all spellings who served in the Confederate Army. There were four "Shellnutt" members of Co. G 40th Georgia, which was formed in Haralson County - James H. (b. 1/4/1841), John B., J.P (b. in Georgia 4/19/1844), and Pinkney (could be J.P., there's almost no info on him).
There was a John Shelnutt in Co. K 34th Georgia, formed in Carroll and Heard Counties (close enough).
There was a J.D. Shelnut in Co. I 37th Georgia, from Campbell, Carroll, and other counties in the area.
The rest of them were from the Walton and Gwinnett counties family(Shellnut).
If the Army got the spellings right, and if the different spellings truly represent different families (something that I have never been completely convinced of), then we can make some assumptions as to who was related to whom.
Of the men I have named, there is no indication that any of them died during the War, although most were wounded. They would have probably been around for the 1870 census. I know this does not directly answer your question, but it does seem to offer some clues.