I'm not sure if this is going to help or just muddle things up, but here goes:
Over the last few years of working on this, I've come across James and Nancy Coile and wondered if they might be the parents of my ggg-grandfather, James Coile, born in NC in 1800, but later moved to Oglethorpe County, GA (which is next door to Madison County - my father was born in Comer, Madison County, but lives just a couple of miles over the county line in Oglethorpe).
I've never been successful in finding anything at all about James Coile's ancestors or siblings.
However, just yesterday I found the Coile entries on the A-D section of the 1860 Oglethorpe County census. James and his wife Mary were listed, as were 10 of their 11 children, with the exception being a daughter whose married name was Martin and thus would've been on another section of the census. There were only two Coiles I couldn't identify, a Joseph T. Coile, whose age was given as "8/12", leading me to think it was supposed to be "8-1/2", and a Nancy Coile, aged 90.
Nancy Coile's name jumped out at me because I know that the other Coiles are my family, and yet here was this lone 90-year old woman on the list. This got me wondering if Nancy Coile was the mother of James Coile. The age would be about right, putting her at 30 in 1800.
The reason I mention this is that I wonder if your ggg-grandmother Mary (Polly) was the older sister of my ggg-grandfather James Coile, and if Nancy was the mother of them both.
Do you have any more information about James and Nancy Coile?