What is the primary source of conflict between Luke and Matt while growing up?

Luke loses his job and the family is left depending on the small amount of money their father left them. This causes tensions that already exist between Luke and Matt to explode. Matt is injured in a fight that seems to parallel the domestic violence going on in the Pye household. Matt is fine and Luke is sufficiently apologetic, but the damage is already done. This leaves the reader fearful of what the future might hold for the Morrison family.