I currently know little that I didn't post. Nancy Alexander and Samuel Dysart married 30 March 1814 in Burke County, NC (bond # 6391). They live in the part of Burke County that became McDowell County, in or near the community known as Dysartville. In 1820, the only Alexanders whom I could find near Samuel and Nancy was the family of Joseph, who was listed as over 45. I hypothesized that he was Nancy's father or much-older brother, and, upon finding the reference to Joseph Lowery Alexander in Burke County, concluded that Samuel's and Nancy's oldest son, Joseph Lowery Dysart, was probably named for his grandfather. It's all conjecture, and, as you state, some of the sons would have been old enough to be Nancy's father.
Both the Burke County Alexanders and the Dysarts appear to have intermarried with the Pattons and with the Woodses in that county or earlier.