Not sure if I will help or muddy the waters more. My GGGGrandfather was Robert Vance. I think he was a brother to your Margaret. According to my records his father was David, married to Elizabeth Colville. and David's father was Andrew(came to America from Ireland in 1680). I received from Patty Evans some documentation that Robert's (and Margaret's) father was Samuel, married to Sarah Colville. I haven't straightened this out yet, but a document she sent me lists Margarets husband as Wm. Lusk. Hope this helps. E-mail me directly email@example.com
and I will give you Patty Evans E-mail address she should be of more help.