Someone who is more into the problems of Robert Abernathy I, Robert Abernathy II and Robert Abernathy III than I is going to have to comment on your Robertson and Tillman issues, but basically the three Roberts are part of a family that arrived in Virginia in the 1650s--probably the result of the annihilation of Scottish forces by Oliver Cromwell's Model Army during the English Civil War.I have concluded that Charles Abernathy (17??-c. 1796) and David Abernathy (17??-c. 1790) are both new immigrants of the eighteenth century, who have nothing to do with the earlier family--at least on this side of the Atlantic.The basic problems are that there is no one for them to descend from, Scotsmen were aliens in English colonies until the union of 1707 that created the entitty known as Great Britain and there was a large Scottish migration and Scottish attempt to make inroads into the Virginia tobacco trade in the eighteenth century.Of course, the newer Abernathys wind up settling alongside the older Abernathys and are much involved with them, and Charles Clayton Abernathy (1790-1877), the grandson on Charles Abernathy (17??-c. 1796), once called David Abernathy, Jr. (17??-18??), a grandson of Robert Abernathy III a distant kinsman.It would be interesting if the relationship were actually maternal rather than paternal!