This is an excellent question because through it you are identifying how Miller has created a separate father-son relationship to act as a foil for the relationship between Willy and Biff. In a sense, Bernard and Biff's relationship parallels Charley and Willy's relationship. Bernard helps Biff academically with his Maths, as his father helps or tries to help Willy financially, by giving him money and then offering him a job. Both Bernard and Charley try to make Biff and Willy respectively face the realities of life. Bernard is always encouraging Biff to study harder and plays almost a father-like role, telling him he shouldn't drive without a license. Equally, Charley tries to get Willy to face the realities of working life. Ironically, in spite of the way that Willy talks about Charley and Bernard, because of their "unmasculine" traits, it is Charley and Bernard that are the success stories, with Bernard becoming an incredibly successful lawyer.
Another central difference that is reinforced through the comparison of these two father-son relationships is how Charley never dwells on misfortune - he is a very down-to-earth and decent individual who is intensely realistic and practical. Willy, on the other hand, is always talking about what could have been rather than facing the reality of what has actually happened. According to Charley, he owes his success to the fact that "I never took any interest in anything." Bernard and Charley both fail to understand the importance of dreams to Biff and Willy and how their dreams sustain them and give them hope. Unfortunately, it is only Biff who at the end of the play is forced to become more like Bernard and face reality for what it is, rather than living a life deferred waiting for dreams to become substantial.