How have biff and happy responded to their father’s condition

Biff denies responsibility for his father's condition, but he is forced to acknowledge that he is linked to his father's guilt and irrational actions. I think happy is just stressed about it.

Biff mentions twice in the play that "Just don't lay it all on me" which he is referring to the state of Willy. Willy was suffering from hallucinations and severe mood swings and Biff very well knew why that was and how & why their relationship had been ruined. (Because of Boston affair) . So for Biff, He tries to confront the truth with Willy and all the family by saying "I'm a dime a dozen and so are you".

Whereas Happy seems to live in an illusion like Willy and tries to feed Willy's illusion and insecurity by impulse not truly intentionally.