Tammy and Ann, In 1903 James Whistler Wood compiled a chart of all known descendants of Major John Whistler,(1758?-1829) the immigrant ancestor and grandfather of the artist.This manuscript is the archive collection of the Chicago Historical Society Library.In the chart is a possible connection to your Robert Ross Whistler.The line goes as follows:
1st Gen. - Major John Whistler m. Ann Bishop 2nd Gen - Edward Whistler m. ? 3rd Gen - Lewis S. Whistler. b 1813; m. Hester Cotrell 4 June 1837 in Vermillion Co., Illinois.They had two sons: 4th Gen - William Whistler, b. 1846 Illinois m. Mary Ross 17 November 1868 in Fayette Co., TX and 4th Gen - Ross Whistler.(Could this be the Robert Ross Whistler you are looking for?)
This branch of the Whistler family moved from Ohio to Illinois to Texas.In the 1850 Fayette Co., TX census Lewis S. Whistler is listed with son William in the household of his brother-in-law Clark L. Moore (husband of his sister Jane).
I have lots more information about this Whistler family if there is a connection and would be happy to exchange info. Cheryl