Here's an excellent account of his ancestors and descendants.

Scotch-Irish immigration to America
Scotch-Irish settlement in the Shenandoah Valley
Tinkling Spring Church

Cowpasture River

James Stewart married Mary Ann Lafferty around 1738 in Ireland, and they came to Shenandoah Valley, Virginia about 1740, settling at Cowpasture in Augusta County. James' older sister Elizabeth (born circa 1718 in Dunblane) married Ralph Lafferty. (They also lived in Augusta County.) Augusta County and Virgina, 1738

James Stewart served as a Captain in the French and Indian War in the 2nd column of the Augusta County Militia under John Dickenson in 1755, and was killed by Indians (burned at the stake) in Staunton, Virginia in September 1757.

Another version reads:

February, 1757 before three of his sons were grown, James was captured with his son James Jr. by Pawnee Indians and burned at the stake, in the presence of his son. The son later escaped. This was known as "Dinwiddie's Massacre."

There's a version of his story here .

His son Ralph Stewart was forced to watch his father die, but escaped. Ralph was born in Cowpasture, Augusta Co. Virginia on December 17, 1749. He married Mary Elliott in 1767. Ralph was a Captain in the Indian Scout Service until the close of the Revolutionary War. He fought under General Nathaniel Greene, and George Washington appointed him one of the guards of Lord Cornwallis after the surrender. Ralph fought at Yorktown under Washington. He moved to Kentucky in 1783 and died in 1835.

There's a couple of pages about Ralph here.