How are Tom and Casy, or Ma Joad and Rosasharn similar? Different?

I think you are right. Both Tom and Casey are easily inspired to fight for change. Tom takes Casey's lead and eventually leaves the family to fight for a better world. Ma Joad's main goal is to keep the family together. Rose of Sharon wants what Ma Joad is so desperately trying to preserve. She wants kids and she wants a family. Of course Ma Joad is far more resilient and world weary than Rose but Rose is just starting out on her path. Casey tends to be a little more relaxed than Tom but also moved to a calling. Once a preacher he finds a new calling in the union movement. Tom takes a little more time to act but eventually he does.