Charley is humble, generous, down to earth, and successful. His extreme character differences from Willy highlight Willy’s flaws of impracticality and arrogance. Willy appears naïve and desperate in contrast to his mature and knowledgeable neighbor.
Bernard achieves the success that Willy wanted Biff to have, and in doing so, highlights Biff’s failure. Growing up as friends and neighbors, Bernard was the nerdy kid who came out on top because he didn’t expect his personality to carry him to success. In contrast, Biff was the popular football star who never focused on his education but relied instead on charisma. As an adult, Bernard is confident and well adjusted, whereas Biff is insecure and unsure how to be happy in life.
As Biff’s brother, Happy grew up with the same parenting, values, and pressures that Biff experienced. But while Biff recognizes and rejects the lies his family has been living, Happy tries to keep them alive. You could say Happy is amoral; he steals his friends’ girlfriends, casually lies to get dates, promotes keeping secrets from his family, and is basically always phony. Biff, in strong contrast, has developed a policy of "no tolerance" for falsehood among the family. Where Biff looks at himself honestly and knows that working with his hands makes him happiest, Happy blindly pursues his father’s ideas of material success.