You are asking some of the same questions that I've had for many years now. In addition to the John Rockett/Sarah Abernathy married in 1787, Richard Rockett married Eleanor Abernathy in 1789, and Sarah Rockett married William Abernathy in this same time period.
Tradition holds that the three Rocketts were siblings, as were the three Abernathys. This certainly appears to be the case, although I have failed thus far to find firm documentation of this. Evidence does exist that implies John, Rickard, and Sarah Rockett were children of Richard Rockett I and Mary Abernathy (who married in Granville Co NC in 1763). Richard I died in Edgefield County SC in 1785, but his wife and children were not specifically named in his probate papers.
This tradition (published in several Rockett family works, in particular the book by Mr. John F. Rockette) emphatically states that Sarah, Eleanor, and William Abernathy were children of James Abernathy and Elizabeth Cox. Moreover, it claims that James drowned in 1785. I spent much effort in the 1980s attempting to find some scrap of hard proof of James & Elizabeth's children, but I was unsuccessful.
I am not familiar with either the Gatewood work or the Avord M. Abernathy book. Can you please send me the references for those works?
To add to your question:
1) Were Sarah, William, & Eleanor Abernathy siblings as some tradition claims? If so, who were their parents?
2) Who were the children of James Abernathy & Elizabeth Cox? Who were the parents of this James Abernathy?
3) Who were the parents of Mary Abernathy who married Richard Rockett in 1763? Their marriage record was signed by Robert Abernathy, a fact that implies he was Mary's father. If so, which Robert was Mary's father?
Do you happen to know why the probating of the will was delayed?