In what ways are Mama and Papa brave in Roll of Thunder, Hear My Cry?

Mary and David Logan of Roll of Thunder, Hear My Cry are strong individuals who display great courage when they take action to fight racial injustice.
(Chapter 1) At the school where Mrs. Logan teaches, the discarded books from the school for the white children are handed out to the class by Miss Crocker. The Logans' youngest child, Clayton Chester, called Little Man, at first refuses the book because it is dirty. But when he sees that all the other books look the same, he reluctantly takes it to his seat. As he looks at the inside cover, he reads the last line in the column entitled "Race of Student" and sees the word nigra written there. Enraged, Little Man hurls the book to the floor and "stomps madly upon it." After he does this, Miss Crocker gives Little Man a whipping; then she reports his behavior, as well as Cassie's, to Mrs. Logan in her classroom at the back of the school. Miss Crocker relates what the children have done while showing her the books. Mrs. Logan studies the books in silence.

"You say Cassie said it was because of this front page that she and Little Man didn't want the books?""Yes, ain't that something?" Miss Crocker said, forgetting her teacher-training-school diction in her indignation. (Ch.1)

Mrs. Logan does not object to the children's punishment since they have disobeyed Miss Crocker. However, she opens her desk drawer and pulls out paper, a pair of scissors, and glue. She cuts the paper to fit the page and glues it over the issue record page with its offensive term. Miss Crocker is appalled that Mrs. Logan would dare to tamper in this way with the books, telling Mrs. Logan she will be in real trouble if someone from the superintendent's office ever sees what she has done. Mrs. Logan laughs and says that no one will come, because nobody from that office wants to see all the other things the poor school needs.
(Chapter 4) Mrs. Logan takes the children to Mr. Berry's house and lets them see how badly burned he is. On the way home, she explains to them that Mr. Berry and his nephews had kerosene poured on them and were burned by the Wallaces. Then she forbids the children to go anywhere near the Wallaces' store. Further, Mrs. Logan stops at several houses on the way home and encourages the adults to not shop at the Wallace store; she also warns them to keep their children away from this place. Afterwards, she and Mr. Logan bravely organize a boycott against the Wallaces' store, and they promise to supply the credit for Mr. Turner and some others if they shop in Vicksburg.
(Chapter 7) Mr. Harlan Granger arrives at the Logans' house after the lawyer Mr. Jemison warns them of the danger of using their land to back the credit for others who shop in Vicksburg. Mr. Granger threatens to do whatever he needs to do "to keep peace down in here." This statement means that he will do everything he can to foil the Logans' plans. Mr. Logan stands up to Mr. Granger by saying, "You plan on getting this land, you're planning on the wrong thing."
(Chapter 9) When pressure is put upon the others who do not own their land as do the Logans, these sharecroppers realize that they cannot afford to have their profits cut on their crops or be evicted. So, they tell Mr. Logan that they must back out of the boycott. Afterwards, Cassie asks her father if they will also quit the boycotting. He tells her that they will not: "We keep doing what we gotta, and we don't give up. We can't." 
(Chapter 12) After Mr. Logan learns that the night men have caught T.J. because they believe that he and two other black boys are the robbers of the Barnetts' store, David Logan springs into action. He knows these men will kill T.J., and he is also afraid for his son Stacey, who is hiding in the nearby forest. As he starts to leave, Mrs. Logan begs her husband not to use his gun, but he tells her, "I'll do what I have to do, Mary... and so will you." As lightning flashes in the sky, he gives his wife a strange look. Not long after he departs, Big Ma, Mrs. Logan, and the others smell smoke. They rush to stop the cotton in their fields from burning. They do not realize that David Logan has surreptitiously set fire to his own cotton field to distract the lynch mob from their evil intentions. And, his plan works because all the men come out—white men and black men—in an effort to prevent total devastation. Consequently, David Logan's bravery keeps anyone from being killed or hurt.