I need to go dig out my notes, but I am thinking your g-g-g grandfather John C. Calhoun (m. Caroline Scholars), is my great grandfather's (Dougal Calhoun) half brother. (I might have added too many greats!) So, Daniel Green Calhoun, my g-g grandfather, is your g-g-g-g grandfather?
You have not researched beyond John C. Calhoun and Caroline Scholars?
I will look in my notes and send later today. I have a lot of Calhoun info.