John Scott, Sr., b. ??, d. abt. 2 Jan 1809 Montgomery Co. VA, married Mary Guthrie 23 Aug 1796 Montgomery Co. VA.
Mary Guthrie was previously married to Ephraim Skyles with whom she had at least two children: Elizabeth and Phebe Skyles. Possibly also Joseph Skyles. Mary's brother Richard Guthrie was appointed guardian of Elizabeth and Phebe on 1 Aug 1797.
John Scott Sr. names the following in his 1809 will: wife Mary, son John, daughters Mary Ann and Jane. Witnessed by Joseph Skiles and Frederick Carper. He appoints his wife and her brother, Richard Guthrie, as executors.
Richard Guthrie turns out to be good clue. He provided surety for John Sr. and Mary's marriage and also for the two children of her first marriage...
Scott, John, and Mary Sykes [sic]. Richard Guthrie, sur. Mar. by Edw. Morgan -- Aug. 23, 1796
Spears, Samuel, and Phebe Skyles. R. Guthrie, sur. Mar. by E. Morgan -- June 2, 1798.
Munsey, Jeremiah, and Elizabeth Sykes. Richard Guthrie, surety -- May 2, 1799.
... and, later, for the marriages of John Sr. and Mary's daughters, Mary Ann and Jane...
Waddle, Alexander, and Mary Ann Scott. Richard Guthrie, surety -- Jan. 3, 1815
Waddle, Alby, and Jane Scott. Richard Guthrie, surety -- Sept. 2, 1818
[Worrell, A Brief of Wills and Marriages in Montgomery and Fincastle Counties, Virginia, 1733-1831]
So you can see that as of 1815 Alexander Waddle was the brother-in-law of John Scott Jr. He provided surety for the marriage of John Scott and Catherine Heavener in 1820...
Scott, John, and Catherine Heavener. Alex Waddle, sur. -- Mar. 4, 1820 [Worrell]
Catherine Heavener was very likely the daughter of Philip Heavener, named as "Catey" in this will...
Heavner, Philip. Will probated May, 1804. Names -- wife, Martha; and children, Jacob, Batsy, John, Sally, David, and Catey. [Worrell]
I believe that John Scott Sr. is the same one who was born about 1738 in Ireland or Scotland and whose father Samuel made oath of his importation into the Virginia Colony in 1740 and died in Augusta Co. VA in 1749. Either that or he is closely related. I am descended from Samuel's son, also named Samuel, b. 1749 Augusta Co. VA, d. 1833 Lee Co. VA. I share a relatively close Y-DNA match with a descendant of John Scott and Catherine Heavener.