What is the Sharīʿah ruling on a father not paying zakat on his money deposited in a non-Islamic bank for 28 years, despite owning lands and a house? And how much is the obligatory zakat if it is due? And is it permissible to give zakat to needy relatives, such as paternal half-siblings?

Depositing money in usurious banks is not permissible except in cases of extreme necessity, and when no Islamic alternative exists. Usurious gains (interest) must be disposed of by spending them on charitable causes. Zakat is one of the pillars of Islam and is not waived by delaying it. Your father must repent and pay Zakat for the past years after an accurate calculation. Zakat becomes obligatory upon complete ownership, reaching the nisab (85 grams of gold or 595 grams of silver), and the passing of a full lunar year (hawl).

If the lands or house are for trade, their value should be estimated, and a quarter of a tenth (2.5%) of their value should be paid as Zakat. However, if they are for residence or personal use, no Zakat is due on them. If the house is for rent, its rental income is subject to Zakat. Zakat paid in one year is deducted from the remaining amount in subsequent years.

It is permissible to give Zakat to needy relatives, provided they are not among those whose maintenance is obligatory upon you, and to needy paternal uncles, or to help them pay off their debts. As for your bank balance, Zakat is due on it if a full year has passed and it has reached the nisab. Usurious interest should not be included in the amount on which Zakat is calculated; rather, it must be disposed of, and the money should be withdrawn from the usurious bank if possible.