Think I'm able to follow, but would appreciate knowing for sure.Am I correct that you are saying as follows?
1) John Abercrombie (c.1736-1816) and wife Ann Kellett (c1743-?)
2) William Abercrombie (c.1769-1855) and wife Saraea Aracey Picard (1772-1816/17)
3) James B. Abercrombie (1807-c.1880) and wife Sarah A. Thomason (c.1810-1865)
Is James "Buck" Abercrombie the same person as James Madison Abercrombie (c.1843-1871)?If so, I have his name in my file as James Madison "Polk" Abercrombie. I do show that James Madison Abercrombie was a son of James B. Abercrombie and wife, Sarah A. Thomason.
Think what is being referred to as the Sims Cemetery is the same as I have listed in my file as the Paul P. Sims Fmily Cemetery. It is puzzling to me if the Sims and Abercrombie families of Chambers County may not have been as close as most cousins tend to be back then.However, do know in more recent times the cousin connections are often not as close as back when.
My wife and I have been to the Paul P. Sims Family Cemetery a number of times and have wondered about the graves without markers. Doubt that I can identify which grave is that of James B. Abercrombie without further help from you.