What Willy taught his children:
Willy Loman essentially instills in his children--Biff and Happy--the importance of outside appearance, of "personality winning the day." In one of Loman's flashback memories, when he is talking to his kids Biff and Happy, he says: "That's just what I mean. Bernard can get the best mark in school, y'understand, but when he gets out in the business world, y'understand, you are going to be five times ahead of him. That's why I thank Almighty God you're both built like Adonises. Because the man who makes an appearance in the business world, the man who creates personal interest, is the man who gets ahead. Be liked and you will never want." Willy tells his children that appearances are more important than talent; he does so by contrasting the studious Bernard--who he says will never be successful--with his sons, who are well built (especially Biff--a football player).
He tells them that success in life is a product of being well-liked, of having a good appearance and charisma, not of being intelligent. Thus, we see his son Biff take these words to heart and not study math (he flunks the class), while Happy continually brags that he is losing weight (again, focusing on the outward appearance). It is clear that Willy Loman portrays his values to his children, and that they have a major effect on Biff and Happy.
Importance of Ben:
Although the scenes of Ben in Miller's "Death of a Salesman" are filtered through the fantasies of Willy Loman (they are subject to his 'changing of the truth'), Ben--Willy's brother--is clearly someone who Willy respects and envies. Willy says: "Why didn't I go to Alaska with my brother Ben that time! Ben! That man was a genius, that man was success...