Scarlett is definitely an S, going by the book, and an ST at that, she's pretty callous at times, so she's no F.
Melinae, and Ashley are N (I can pull out quotes from the book, but I'm too tired tonight,) and as much as I hate to admit it they are probably both INFP in my opinion, although Melanie has decidedly more back bone than her husband.
Rhett is an N, he had said that Ashley and himself actually had view points in common in the book. I lean toward ENTP myself, but ENTJ works too, I just see more Fe at work behind the scenes than Fi (i.e. trying to win over the confederate families for his daughter Bonnie's sake. If you've read the book, you'll see what I mean.)