A descendant, Bob(F-34), of James and Agnes (LINDSAY) FAIRBAIRN is an excellent yDNA match (67/67) to descendants of John and Magdalen (BO) FAIRBAIRN, but where James "fits" into that tree is completely unknown.
As Alexander is a family name for Bob's line, perhaps there's a link with one of the Alexanders contemporary with the John of Stewart's line, and possibly there is a connection to one of the early Alexanders in Mellerstain, Earlston?
It may be possible to confirm family relationships with James by comparing test results with other
carriers of his Y-chromosome or his mother's mitochondrial DNA.
Y-chromosome DNA test-takers in his direct paternal line on WikiTree: