Allison Family Mysteries in VA

Profile manager: Roxy Mitchell [send private message]

William Allison lived in Fauquier County, Virginia from approx 1775 to 1839. I have a copy of his will where he lists his wife and children. His wife is listed in the will as "Nancy" but I can find no one by that name marrying a William Allison. I do see references to a Mary, possibly maiden name of Clark. Can anyone confirm this? Also I am unable to find anything about his parents. Several other trees list his parents as John Allison and Margaret Spencer. However all of them indicate that John's first two children, Richard (1773) and William (1775) were born in Fauquier County where they lived and died. The rest of his children were born in Carrabus NC. Why would he have left 2 small (under 6 years old) children in VA and moved to NC? That link does not make sense and I am unable to find anyone else to link him to. Any ideas?