There is an extensive history given in The Swearingen Family Register:http://www.archive.org/details/familyhistorical00swea
It does list John R. Swearingen's parents as William D. Swearingen and Sarah "Sallie" Ray. It is likely his middle intial stood for "Ray," as that is the name of his grandson, John Ray Swearingen, my g-grandfather.
Interesting to see that William C. is indeed mentioned as a brother of John R. ... William is very famous in Texas as a hero of the Texas Revolution and as an early Texas Ranger. There is a monument to him in downtown Houston, TX. He wrote a famous letter to his brother Lemuel.