As a Madison descendant you can possibly "persuade" your cousins to DNA test William, son of Madison, against that of Eston to see if Madison and Eston have the same fathers. William did not have children. It is my belief, based upon deep research, that they will not match. Sally's mother, as you possibly are aware, had several children by different fathers. IF there were different DNA between Madison and Eston that would also indicate that Sally's children had different fathers. Why not test and arrive at some scientific conclusion?
Does your family use the spelling, "Hemmings"?