The Question and Answer section for Roll of Thunder, Hear My Cry is a great resource to ask questions, find answers, and discuss the novel.
He had sworn to Pappa that he would protect the family. He also loved the family as well.
I don't know if it is explicitly stated but I think they are worried about retribution over what T.J is blamed for and basically everything that has gone on. A storm is coming in more ways than just the weather.