As for Catherine, daughter of John Snapp and Mary Ann Windle, I haven't researched this family and can't help make the connection to Catherine who married Jacob Spillman. You may already have seen that the Ancestral File has a marriage to Joseph Thornton for the first Catherine. For the second Catherine there are posted Snapp trees, such ashttp://wc.rootsweb.ancestry.com/cgi-bin/igm.cgi?op=REG&d...
that say John Snapp and Catherine (? [others say Fry]) are her parents.
Your second request is covered in "Frederick County, Virginia: Settlement and Some First Families of Back Creek Valley 1730-1830," by Wilmer L. Kerns, Ph.D. (Gateway Press, 1995), p.221. I've attempted to set a visible e-mail address, but if that doesn't work a temporary one is: email@example.com
. I can e-mail the few pages I have from this book.