I have a fair bit of info on the York SC Darwins, but the dates don't quite marry up with what you have.I show Mary Darwin as born 16 May 1785 and dying ca. 1856 (birthdate matches well her age as given in Federal census returns); I also show her husband, John Kendrick, as born in 1771.
Mary Darwin was the daughter of John Darwin (19 March 1755-13 July 1837) and Jane Bland (2 January 1762 - 10 March 1827).John was born in Louisa County, VA, son of William Darwin (1707-1786) and Jane (?Wilkerson); he served in the 3rd Virginia Regiment, Continental Line for two years, during which he participated in the battles of Harlem Heights, Germantown, Brandywine, and wintered at Valley Forge (his own account of his service has survived, and is available from the US Archives). He followed his older brother James to York District SC, and continued in revolutionary service as a partisan there.His wife's brother, John Bland (1758-1781) was also a partisan for the American cause in South Carolina, and was killed at the Cloud Creek massacre.
The full family of John Darwin and Jane Bland:
1. Nancy (1784-1847), married Jephtha Harrington 2. Mary (1785-1856), married John Kendrick 3. William (1786-1862), married Elizabeth Powell (moved to Tennessee 4. Rebecca (1780-1842), married John Moore 5. Rachel (1790-1831), married John Powell 6. John B. (1791-1854), married Gilly Sandlin (these are my own 3xgreat grandparents) 7. Jane (1794-1856), married John Smarr 8. Robert G. (1795-1867), never married 9. Matilda (1797-1848), married William Berry 10.Sarah (1801-1802) 11.Pamela (1803-1880), married Isaac Summerford 12.Peyton B. (1805-1883), married (1)Mary Wilkerson (2) Jerusha James
I have a good deal more on many of these folk; please advise if of interest.But I have not looked into family of Mary Darwin and John Kendrick, would be interested to see the tree of their descendents. Hope this is of some help.