You may know that William C. Marsh shot and killed St. Clair Young in July 1850.Marsh was acquitted of murder, but was subsequently ambushed and killed by St. Clair's son, Stanley Young, in 1858.
I have found two versions of the story.The first is in "Life of Walter Quintin Gresham, 1832-1895," Matilda Gresham, Chicago, Rand, McNally & company, 1919, at page 29.This version does not mention any relationship between St. Clair Young and William C. Marsh.
There is a second version of the story in "Confederate guerrilla Sue Mundy : a biography of Kentucky soldier Jerome Clarke," Thomas Shelby Watson and Perry A Brantley, Jefferson, N.C., McFarland & Co., 2008, at page 43. In this version, St. Clair Young and William Marsh were brothers-in-law, but there are inaccuracies in story that make me cautious about trusting it 100%.
This isn't my family, so I do not have information one way or the other about a possible relationship between the men. I do know that Sarah Armstrong was not St. Clair Young's sister.In addition, St. Clair was married to Amelia Hammond. Perhaps Sarah and Amelia were half-sisters--assuming the brother-in-law story is accurate.