Ellyn, Jane again, I was just looking at this old message from you. Do you have a date of birth for David or death of his wife, Sarah Blackstone? Do you think David might have had two wives? Sir Wm. Short's will proved Oct.1769 Brunswick Co. VA proves marriage of his daughter(no name Short) to David Abernathy. Reference:Marriages of VA families 1607-1800 --D.F. Wulfeck Vol.1
The dates look too late to be David (married to Sarah)'s parents, don't you think? Have you other children for David and Sarah or did she die after the birth of the two boys?