Eleanor, the daughter of James Alexander who d. in Rowan County in 1853, married Samuel Rankin. This line is fairly well documented with land and court records. I could put you in touch with a direct descendant of Eleanor & Samuel who is a very careful, superb researcher. But it doesn't sound as though this is the right line for you.
I would definitely pursue the John McKnitt Alexander and Jemima Alexander Sharpe connection to your Parker line. John McKnitt was a "shaker & mover" who seemed to be everywhere - and not just in Mecklenburg County but also in Lincoln and Burke Counties. Probably elsewhere also - I just haven't had reason to come across him in other places.
I do have (UNPROVED!!) in my notes that Jemima Alexander (b. in 1726) m. James Sharp. She was a sister of John McKnitt Alexander:
James Robert Alexander b. ca 1690 Somerset County, Maryland m. Margaret McKnight (McKnitt) b. 26 Dec 1693 Somerset County, Maryland Their children included Theophilus, Jemima, Edith, Keziah, Ezekiel, Hezekiah, Amos, John McKnitt, Margaret.