What is the ruling on money taken by siblings without the questioner, and is it permissible to demand it back? Does paying Zakat on behalf of the deceased absolve them of the pillar of Zakat? What is the ruling if the children pay Zakat for past years? Is it permissible to give Zakat money to married, non-dependent children? Is it permissible for non-dependent children to take money from interest to pay off their debts?

Regarding your father:

1. Placing his money in usurious banks and taking interest is forbidden and is considered among the major sins.

2. Giving his children money from interest:

If their maintenance is obligatory upon him: It is forbidden, because it is benefiting from prohibited interest.

If their maintenance is not obligatory upon him: There is no harm in him giving it to them to dispose of it due to their poverty, and you have no right to claim a share of it.

3. His not paying Zakat is a major sin, and the heirs must pay it on his behalf before dividing the inheritance. If they have already divided it, then each heir must pay Zakat from their share.

4. The treatment of a father who favors some of his children over others in giving gifts is forbidden according to the preponderant opinion. It is obligatory for the child to honor his father and be kind to him.

5. It is permissible to give children from Zakat if their maintenance is not obligatory upon the father. Similarly, giving poor children money from interest to pay off their debts, in order to dispose of it, is permissible, along with repentance.