UPDATE: It now seems certain that William Davidson and Martha Baker did not buy land from the Murray family in Botetourt Co., VA in 1774. That was a different and unrelated (per DNA testing) William Davidson who came to VA from PA (he married Sarah McCoy and the widow Mrs. Elizabeth (Wilson) McCRea). It now appears that William Davidson and Martha Baker bought land in Botetourt by 1779 (and their land never became part of Rockbridge Co., VA, it appears).
Also, the Joseph Davidson (died 1820s) who married Jinny Wilson was out of the above-referenced William Davidson from PA (whose land in Botetourt became part of Rockbridge Co., VA in 1778). The unrelated Joseph Davidson (died 1814), who WAS a son of William and Martha (Baker) Davidson, apparently died without a wife or children.
The Thomas Davidson who I showed as a possible son of William and Martha (Baker) Davidson now seems to have been from yet another/third Davidson/Davison family in the Botetourt/Rockbridge Co., VA area (per DNA testing). Also, the Elizabeth "Betsy Ann" Davidson who had an affair with a David Smith MAY have been out of that unrelated Thomas Davidson, versus out of William and Martha (Baker) Davidson (based a couple "clues").
Based on tax lists in the 1780s in Botetourt, it appears that William and Martha (Baker) Davidson had an oldest son whose name is not proven....and who seems to have left Botetourt (or died) by 1785. The four younger known sons were 1) Baker Davidson, 2) William Davidson, Junior, 3) Rev. Andrew Baker Davidson and Joseph Davidson.