I too am related to the Charleses of Llanddeusant. Your search for "Charles" graves in Llanddeusant may not be returning copious results because of the Welsh patronymic naming sytem. The earliest ancestor in the line whom I can trace is Morgan Charles of Llanddeusant (d.1770), via his son, Charles Morgan. You see, in this instance, Charles adopted his father's christian name - Morgan - as his surname. Very few generations before their time, we would have used the patronymic possessive "ap", meaning "son of", to convey belonging. E.g., Charles, son of Morgan, would have been Charles ap Morgan. It was very important for the son to be known through a pater familias from a long-established local family. It wasn't long before the start of the 17th C that the use of the conjunctive "ap" was abandoned, but the convention remained intact through adopting the father's first name as a 'surname'. (It was the English court system which arrogantly asserted that this system, too, should be done away with, although we doggedly persisted with it for generations in quiet defiance).
Morgan Charles had many children, although it would seem that your line retained the Charles name, which would suggest that it crystallised a little bit earlier with your ancestor. Many of the Charles clan stayed for generations in nearby areas such as Bethlehem and Gwynfe, and their graves will likely be found there.
