Does a son's giving of charity from money taken by his father from postal interest and distributed among his children alleviate the father's burden of sin?

You are not permitted to accept usurious interest from your father. You must dispose of it by spending it on the welfare of Muslims. Your father should be advised gently to repent from taking these interests, and the severe warnings associated with them should be explained. If the father has passed away, then disposing of these interests benefits him as a repayment of debt and a restoration of rights. He also benefits from supplication, seeking forgiveness, charity, and performing duties that accept proxy.