Y-DNA proves Landon Carter of Watauga and the descendants of the males of the Virginia Carter families could not possible be related. According to the Carter Society Y-DNA Project: the male descendants of Thomas Carter of Lancaster belong to Haplogroup R; the male descendants of John Carter of Lancaster Y-DNA are also members of Haplogroup R.
The Y-DNA tests of the male descendants Landon and his brother John, shows their Y-DNA to be Haplogroup E. Totally separate haplogroups could not be of the same male linage.