You may find some help here -- read the sections on the characters.
P.S. Here are some other sites on that book:
1. (Wikipedia): http://en.wikipedia.org/wiki/Roll_of_Thunder,_Hear_My_Cry
2. (Study Notes): http://www.gradesaver.com/classicnotes/titles/thunder/
4. (another Study Guide): http://www.aloha.net/~uncldon/rothmyc.htm
5. (book notes): http://www.bookrags.com/notes/roth/
As for comparing with characters from another book, you will have to select another book you have read.