Is it permissible to give Zakat from business money, which I have the authority to dispose of and even to give Zakat from, to my father who has a limited income and supports a family, knowing that this money will be used to build a house?

The basic principle is that it is not permissible to give the parents' Zakat on their wealth to their children whom they are obliged to support, because these children are considered rich by virtue of their maintenance, and giving Zakat to them would bring a benefit to the father by exempting him from the obligation of Nafaqah (financial support). The father's obligation to support his son continues until the son reaches adulthood and is able to earn enough for himself and those he supports. If he is capable of earning but cannot find suitable work or what he earns does not meet his needs, then the Nafaqah remains the father's responsibility.

Accordingly, it is not permissible for the grandfather to give Zakat to the father due to the grandfather's obligation to support him, except for the purpose of settling the father's debts. As for the Zakat on the uncle's wealth, it is permissible to give it to the father because the uncle is not obliged to support him.