Good question about where in NC Joseph came from, but my info does not tell me that.
I can tell you this regarding the yDNA of this descendant of Joseph and Barbara.His DNA rather distantly matches 6 others in the Alexander DNA Project.None of the 7 closely matches another.So the strong presumtion is they are all related through people born in Ireland or Scotland, rather quite before immigration to the New World.
The closest match of this member is a genetic distance of 6 based on 67 markers.That match has reliably traced himself to a James Alexander b. 1706, Campbeltown, Scotland m. Jean (recorded as Jane in church documents) Reid d. 1771, York Co., PA.
The son of this couple in this line is James Alexander b 1733 Campbeltown, Scotland, m (1) Margaret Wilson and (2) Margaret Clarke Ross, d May 9, 1817 Belmont Co., OH(family moved to OH in 1803).
Based on their DNA, the probability these two members shared a common ancestor in the last............ 8 generations is 15%. 12 generations is 45%. 16 generations is 73%. 20 generations is 89%.
Must caution these are AVERAGES based on a database of hundreds of thousands, but it still gives you a flavor.