Is it obligatory for children to calculate the usurious interest their parents took from banks, and is it obligatory or recommended to give it away in charity to absolve the parents of sin?

The sin of parents dealing with usurious banks and consuming their interest depends on the motive. If it was due to a belief that the one who issued the fatwa was correct, then they are hoped to be forgiven, for the Prophet, peace and blessings be upon him, said: "Whoever is given a fatwa without knowledge, its sin is upon the one who gave the fatwa." However, if it was out of following whims and being lenient, then expelling the interest from their estate does not absolve them of the sin, but it benefits them by dropping the claim for this money. The children should increase in seeking forgiveness, supplicating, giving charity, performing Hajj and Umrah on their behalf. As for the inherited money, the heirs must determine the origin of the lawful money and the amount of usurious interest, and then dispose of the interest by spending it on Muslim welfare or giving it to those in need. This is the preponderant view. Some scholars are of the opinion that unlawful money due to its acquisition, not its essence, is unlawful only for the one who acquired it, and it is not unlawful for whoever acquired it from them through a permissible means. According to this view, the heirs are not obligated to remove the usurious interest from the inheritance.