You will find William R. Forbess with his parents & siblings in the 1850 Sullivan, Tn. census with the last name of Fauless.

The census is as follows:

1850 Sullivan, Tn., 1st Division, page 35

Fleming Fauless, age 38, b. Va.
Cary Fauless, age 39,b. Va. (This is Clarissa Swanson)
Daniel P. (I'm not sure about the middle initial) age 16, b. Va.
Peter, age 14, b. Va.
Louisa, age 12, b. Va.
Wm., age 10, b. Va.
Mary Mahaffey, age 8, b. Va.
John, age 2, b. Va.

The Louisa shown above is probably the Louvinia Snyder shown in Kanawha, Wv. as the daughter of Fleming Forbess.

I have found no evidence that the middle name of William R. Forbess was Riley. I know that his son was named William Riley Forbess.