How should an heir dispose of money from his father and mother that was deposited in a Riba-based bank? Can he atone for their sins? And are the bodies of the heirs considered to have grown from illicit gain?

If the questioner did not know that what she inherited was acquired through illicit means, then there is no blame upon her in benefiting from it, and it is lawful for her. However, if she knows that it contains unlawful money, such as usurious gains, then she must dispose of it by spending it on the welfare of Muslims or giving it to the poor and needy. Ibn Rushd Al-Jadd mentioned that inheritance does not purify unlawful money, and Al-Nawawi stated that inherited money whose source of acquisition is unknown is lawful by the consensus of scholars. As for eating from the parents' food, there is no harm in it as long as their money is mixed and not entirely unlawful. It is recommended to frequently seek forgiveness and supplicate for the parents, and to establish something as an ongoing charity for them.