Is there any sin on anyone—the grandfather, or the father, or the questioner, or the brother—due to an interest-bearing deposit that the grandfather deposited for the grandchildren, and then the questioner waived it for his father to buy an apartment for his brother, and the questioner took possession of one of his father’s two apartments in return for that?

Whoever deposits usurious funds or takes their interest, believing it to be permissible based on a reliable fatwa, is excused due to their ignorance and reliance [on the fatwa]. The sin for this falls upon the one who issued the fatwa, for the Prophet, peace and blessings be upon him, said: "Whoever is given a fatwa without knowledge, his sin is upon the one who issued the fatwa." As for whoever deposits or takes it while knowing its prohibition and believing the fatwa to be erroneous, the sin is upon them. Usurious interest must be disposed of by spending it on charitable causes for the poor and the needy. A poor person in need may take from it according to their necessity.