I have studied these Carters for many years as my Gilliams (Carter Gilliam, etc.) were their namesakes and intermarried with them.
As to the two Elizabeths. . . Generally in the records the "Elizabeth" who married Charles Manning Gilliam is referred to as Eliza A. where as the other "Elizabeth" is referred to as Elizabeth M. being named after her mother.
My Gilliams lived on the branches of the Willis River near the "Fork" in Cumberland.
When trying to sort out these Carters, it should be noted that in 1730 a John Carter patented 9450 acres in "the fork" of James River then in Goochland, that in 1748 a Robert Carter lived near a Ferry that was opposite the mouth of the Willis.
Virginia Ferry Operators, 1748 From the land of Ashford Hughes, on the north side of James river, near the mouth of Willis's creek, across the said river, to the land of Robert Carter; and from the said Carter's to the said Hughes.
Also James Gilliam Jr. purchases land from John Carter and Susannah his wife in 1784 in Cumberland. This John Carter leaves a Will in Cumberland dated 14 Jul 1814 which mentions wife Susannah.