Cynthia, It certainly does sound like this is the right Ferguson family for you to be searching. So you're saying that your ancestors were slaves of these families? Who was Ann Chalmbers? William was the only one of James Chalmers's sons stayed in Alabama after the Civil War. I have some limited information on his family, I'll look for it and send it to you.
I think that some of the Cotton family lived in Mississippi, but I'm not sure about the Fergusons. It might be a good idea to look at the William Ferguson, brother of Bryant, family to see what happened to them after the Civil War. I have only don limited research on the Fergusons.
I would love to see those letters. Where can I find them?