How do the Ewells (Bob and Mayella) exhibit courage during the trial?

One of the authentic aspects of Harper Lee's novel "To Kill a Mockingbird" is the portrayal of the small Southern town and its types of residents.  Within the poor community, for example, there are those like the Cunninghams, and then there are those like the Ewells.  The Ewells are at the nadir of the socio-economic stratum; they are those that are often referred to as "white trash," whereas the Cunninghams are simply poor.  The Cunninghams are the type of family that still retains some human dignity; they repay a debt by giving a person something from their garden, or working for the person they owe.  When Walter is asked why he does not have a lunch, he says nothing.  When Mr. Cunningham is addressed politely by Scout, he shows respect for her and her father and is ashamed that he is part of the mob before the jailhouse, and he directs the others to join him in departing.

However, no Ewell would do such a thing.  The Ewells possess no redeeming qualities.  Their behavior in the courtroom is not courage; it is a type of perverse bravado meant to justify to themselves their behavior and conceal from their audience what they really are.  Steinbeck wrote, "The less a person has, the more he feels the need to boast," and this is true with the Ewells who have no redeeming qualities. For instance,  Mayella repays Tom Robinson's kindness with open contempt; if she had any "courage," she would have spoken differently in the courtroom.  Mr. Ewell shows nothing but depravity in his behavior.

The distinction between these two types of families is explained in Chapter 3 Scout talks with her father about the Cunninghams and the Ewells.  Atticus explains the difference: 

If he held his mouth right,Mr. Cunningham could get a WPA job, but his land would go to ruin if he left it, and he was willing to go hungry to keep his land and vote as he pleased. Mr. Cunningham came from a set breed of men.

But Atticus tells Scout,

...the Ewells had been the disgrace of Maycomb for three generations.  None of them had done an honest day's work in his recolllection....They were people, but they lived like animals. 'They can go to school any time they want to, when they show the faintest symtom of wanting an education...[they] were members of an exclusive society made up of Ewells....when a man spends his relief checks on green whiskey his children have a way of crying from hunger pains...but he'll never change his ways.