I found a photocopy of the Robert Kinkead Bible! Robert was a son of David/Mary Williams. He was born May 6, 1803 and died December 27th 1845. He married Polly Ann (possibly Merrium) August 31, 1826.
She was born January 8th 1805 and died August 19th, 1893.
Ben Kinkead, in his letter refers to land deeds he had in Sullivan County TN and a deed for sale by David Kinkaid, executor of Joseph Kinkaid dated Feb ?? 1797, which appears to tie into one of the land. records. He says that his grandfather, and his father David Jr. and possibly "short" David (m. Mary Williams) are all buried on this land.
http://archiver.rootsweb.ancestry.com/th/read/KINCAID/2004-03/1080615204