First, the published flawed data:
From Morton's History of Highland Co (not complete nor entirely correct):
I have never seen evidence of Jehu's existence, nor primary evidence that John's wife was a Pickens. Several children are missing from this list.25142

Married Mary (Pickens) Callahan, widow of Wm Callahan. [Cleek, p.96] No marriage bond for this John in Bath Co and Mary doesn't match wife's name of Rachel in 1850 census. Cleek may be wrong, or John may have married twice. Elsewhere, Cleek has a John Givens married to Rachel Pickens, so perhaps this John's wife really is a Pickens. If she's his first wife, they were married before about 1813.
William CALLAHAN and Mary PICKENS were married, 3 Feb. 1812, at Pendleton Co., Virginia, by Otho WADE. [Pendleton Co marriages, from Bird page vol 5 on Bath Co page)25142