I too am descended from Henry and John Mullan, but all the info I have on them does not link them to VA or Scotland. All I have is that they are all from Pennsylvania and I got this from the LDS Website.
My link to this family is John's son Henry Harvey. He had a daughter, Mary Lindsay Mullan and this is my G-G-Grandmother.
In my family there is the rumor that Mary was Indian. Do you have any such similar rumors in your line? Her son, his daugher and my father are all dark complected, dark hair - does this ring true in your line?
Please feel free to reply to this posting or email me directly at firstname.lastname@example.org. Thanks!