I have never found evidence of another Thomas Carter in Amelia around this time. The name Thomas Carter seems to show up in Amelia documents right around the time of his marriage and is gone after 1828. It sure would be a coincidence if there was another Thomas Carter present only during those years as well and is not present before or after. The census records back this up too.
It seems like there is only one Thomas Carter interacting with Joseph Haskew. He serves as substitute for Joseph Haskew in the militia in 1814; his wife, Catherine Muse, and children then are settling with Joseph Haskew over Thomas' debts after Thomas' death, as stated in the chancery documents. The executor of Haskew's will in 1843 was John's son, William Ryland Carter.
Whether the Thomas, son of David Carter, is this same Thomas, is not clear from the chancery documents. The fact that Jesse Walton shows up on separate documents, interacting with John and this Thomas Carter could be coincidence; seems unlikely, but I cannot be certain.
Similarly, I have never found any evidence of a second John Carter in Amelia during my John's lifetime (1775 - 1852). The ledger of John's son, William Ryland Carter, give me John's birth date of March 25, 1775, but I have found no records of John in Amelia until 1801, when he is contracted to build a bridge at the property of Gardiner Mayes. There is only one John Carter in Amelia on the census in 1820 - 1850. There is only one Carter in Amelia on the 1810 census, a Mary Carter (head of household) who is an older woman, living with younger family members (relation to John unknown). The chancery documents show that John was living in Ligon Town in Amelia in 1809 (the year his son William was born), but no additional data.
On a deed from 1813, when John Carter sells 1/2 acre in Clementown to John Booker (which he bought from James Vaughan in 1803), he is listed as living in Cumberland County. Now in Cumberland County, there are no shortages of John Carters.
There are a couple of other Carters kicking around Amelia, whom I have not been able to identify. On the 1820 Census, there is a James Carter. I have never found any other references for him. Also in 1818, Jane Carter acts as surety on the marriage of Mason Wingo (daughter of Allin Wingo) and James Bell. James Bell is mentioned many times in the day book I possess of William Ryland Carter (John's son), which makes me think there may be some connection, but I yet to find it.