Yes, Milly was born in 1800 - but there is absolutely no proof that Anna Elizabeth, Mourning, and Jane Blankenship were Milly's sisters. Nor is there any documentation to substantiate that Milly was a Thompson, let alone the daughter of a Captain John Thompson. I do believe Anna Elizabeth, Mourning, and Jane Blankenship were John Blankenship's daughters. They are mentioned in at least two Coosa County court records as the daughters of John Blankenship. In addition, all four females (Milly, Anna Elizabeth, Mourning, and Jane) appear, age-correct, in the 1830 census of Shelby county AL where John was listed as head of household. In 1860, Milly lived with her daughter Margaret, and next door to Anna Elizabeth Blankenship White. There was definitely a connection between the two women as Anna Elizabeth, following her marriage to Armajor White, named her eldest daughter Milly.
Milly is documented in court records as having relinqueshed her dowry following John Blankenship's death in 1857 - I find it odd that a Cherokee woman would have had a dowry. In addition, the Blankenship, White, and Thompson families had early land grants in Alabama - all three of these families stem from Virginia Revolutionary War pensioners. What their connection is to the John Thompson of Cherokee fame, I do not know. There was a John Blankenship listed in the 1820 census living at Rutherford, NC, in the same proximity to Richard White and John Thompson - were these Cherokees or mixed blood? There was also another John Blankenship, living at Clarke county, GA in 1820. Since Milly was born in GA in 1800, as was Anna Elizabeth in 1817, I think it is this John Blankenship who moved by 1830 to Shelby county, AL.
There actually may have been two John Thompsons - one a minister, a missionary in the Cherokee region and the other John Thompson a Cherokee interpreter who served with Ridge & Ross. Both John Thompsons are reputed to have helped relocate Cherokees during the evacuation. To date I have found no source documentary evidence that one, or both of these John Thompsons permanently relocated to Coosa county, Alabama. Rather, if you look at the Cherokee rolls in AK, OK and TX you will find John Thompson, Martha Fields and a Milly Thompson there with a long list of Cherokee descendants.
If you have any documents, old letters, or information to help me sort out the confusion about the Blankenship, White, and Thompson families I will be most appreciative.