I think it is a cinch that Mary William was Gabriel's daughter. Gabreiel is the only Goad associated with Casey County.He left Sullivan County, Tenn a bit aheasd of the rest of his family. His brothers, and maybe mother And sisters. went to Hopkins County, Ky and spread out from there. Only the older brother Wkll stayed in the Sullivan area.
The Sally (Sarah) Willians is an almost sure ber for Gabriel's seconf wife who was SDarah.
Gabriel was first in Lincol County, Ky from which Casey was formed in 1807. (you said that).