Explain the relationship between Hally and his parents, and Sam's role and his influence in Hally's life in "Master Harold"... and the Boys?

Based on the conversations that Hally has with his mother over the telephone regarding is father's condition, the audience gathers that Hally has a strained, distant relationship with his parents.  It is apparent that Hally's father has a drinking problem, one likely brought on by his inability to properly cope with his physical disability.  Hally's mother does not stand up to his father, and instead she tries to appease Hally's father and to make him comfortable.  Hally appears to be ashamed of his father's lifestyle, and he is angry at his mother for "allowing" this to continue.  Sam recalls times when he took Hally out to play because the father was unable to do these things with Hally.  Sam serves as a father-figure in many ways for Hally--he tries to teach him the life lessons that his father is unable to teach him.  Near the end of the play, Sam reminds Hally of all these times and he makes Hally aware of the realities that he never noticed because he was too small (i.e. Sam not being able to sit on the bench with Hally because it was a "whites only" bench).  Sam wants to teach Hally to be a better man and to resist the injustices of their society.