Richard Harvin III married Elizabeth Ragin Broughton's sister Frances Ragin. I believe that Elizabeth and Frances were about four years apart in age, not that it meant much in the late 1700's.
Despite the apparent confidence that my posts seem to indicate, my sources are really pretty sketchy. I am hopeful that I will have some new information soon (within a few weeks) and I'll be happy to share it with you. So far I have only the mention of the Broughtons in the will. The Cannon connection looks interesting; I'll let you know if I can find anything.