when linda says to her sons that "attention must be paid" to willy, who sould be paing attention?

She is talking directly to Biff in this instance.

Since Linda does not specify anybody in particular to pay attention, she is trying to inspire their basic human feeling rather than ordering them to see their father in a different way. This seems to work, particularly given that they become concerned about his suicidal actions and try to give him some hope that Bill Oliver might launch the family back into success.

Sorry to disagree....... the coversation includes Linda and her sons... at this point in the dialgoue Happy is defending Willy and Linda is speaking to the son she hasn't been able to get into contact with. I'm sure it didn't hurt him to hear it, but it wasn't directed at him.