Thanks for your note. I really enjoyed the years that I conducted in-prison seminars for Prison Fellowship. I found that the story of Joseph (from about Genesis 37
through chapter 45) to be powerful with those “inside.” At the outset they identify with Joseph, who has been wrongly imprisoned. Toward the end they see that they identify more closely with Judah (the one through whom Messiah would come, who needed to repent, and did. From Joseph they come to see what true forgiveness looks like.
I would also be inclined to do a study in one of the gospels (Luke and John are favorites), and a study of the Book of Romans.
From there I would probably be inclined to teach 1 and 2 Corinthians.
Another profitable study is in 1 and 2 Samuel, with a focus on the life of David.
In terms of doctrine you could look at Hampton Keathley’s “ABC’s”