I've found convincing arguments, but not enough sourcing, for both Mary Paxton being the wife of Alexander Stuart and mother of Eleanor Stuart Walker, and also for Mary Moore (b. 1736 PA - d. 1805 Brownsburg, Rockbridge Co., Virginia). Part of me wonders if he married two Marys?
I'm posting in hopes that a descendant with more insight might want to jump in. What do you think?