In your message you indicate your family line is down from Robert C. Alexander, son of Joseph Lowery Alexander. My husband's line down through another of his son's, John Piper Alexander. Have you found out anything about this man?
I know that Joseph and Margaret Tate were married in Pennsylvania and that her family (Sam Rock Tate) sailed over in their own ships from Ireland. Family tradition says alexanders came over with Tates but I can find nothing to prove or disprove this statement.