I have found some info on a William Sisson that appears to be part of Richard and Mary's line, but I am not sure exactly where he fits. English Estates of American Colonists 1700-1799, Volume 2. Sisson, William, of Newport, Rhode Island, and of Lieutentant- Colonel Hargill's Company of Rhode Island Regiment of Foot, who died at Havana, bachelor. Administration by his solemn declaration to Joseph Sherwood, attorney for mother, Deliverance Sisson at Portsmouth, Rhode Island. (Dec. 1765).