You have picked a good topic and one around which you should be able to formulate a good thesis with the works you have listed, as well as others. Think about the main characters in Gaines' novels and whether or not they have experienced redemption from being racially oppressed in the various novels. Perhaps your thesis could revolve around how specific characters have been racially oppressed and then redeemed. For example, in one of the works you have cited, The Autobiography of Miss Jane Pittman, Jane's family and Jane herself underwent incredible racial oppression throughout life. All the while, Jane always wondered who the one was going to be that would redeem the people. She thought it might be her adopted son, Ned, but he was killed, then she thought it would be young Jimmy, but he was killed. Finally she realized, SHE was the one -- it was her responsibility to stand up to racial oppression.
So, I think a good thesis could revolve around a character study - i.e., How Ernest Gaines uses characters to illustrate that it is the individual's responsibility to redeem himself/herself from racial oppression.
Some other teachers may offer you some additional advice, hopefully. There are lots of possibilities. Good luck.