1)What is the source for Thomas b. 1766 and Zachariah b. 1760? 2)What is the source that they are brothers?
What we know: A. The Bryan, Boone, James Chapman, Samuel Waggener,Jr. and Erasmus Withers Allen families all lived near each other near the Forks of the Yadkin river.Erasmus moved there abt 1770.Jesse Bryan witnessed Erasmus' will.
Thus, we can be pretty sure all these families were well acquainted with each other most being related by marriages.
B. Some Thomas Allen married Marjore Bryan May 26, 1789.The marriage record doesn't name his parents.
C. Your source indicates the Thomas who married Majore had a brother Zachariah.Assuming your proof, then we have the following candidates for that Thomas:
While Erasmus had sons, only William had sons born in the right time frame but no Zachariah.Erasmus' other sons are too young to have children in those birth years.And his son Thomas is older than your record.(By the way Streshley Allen moved to KY, but we've never tied him to the Streshley born abt 1790.Any ideas.)
Erasmus Withers Allen has brothers James, Thomas, Zachariah and Andrew whose lines I do not have.Any of these could be the grandfather of the Thomas and Zachariah you mention.My first choice to research would be Zachariah. Certainly, it's probable that the Thomas and Zachariah Allen met the Bryan family because they visited their Uncle or great uncle. D.While early records are in Rowan County, later counties were split from it.Perhaps Thomas and Zachariah Allen's father stayed in NC and shows up later in one of those counties.