Is it permissible for me to give my zakat to my brother who is unemployed and going through difficult health conditions, especially since his son has returned to live with him, knowing that he is somewhat extravagant? And is it better to give him money or to buy what he and his son need?

It is not permissible to give your brother zakat if his poverty is a result of his extravagance and not due to a lack of money, because he is not among those eligible for zakat. A faqir (poor person) is one who cannot find sufficient means, and a miskin (needy person) is one who finds some but not enough. As for one who is poor but able to earn, zakat should not be given to him, as the Prophet, peace and blessings be upon him, said: "Charity is not permissible for a rich person, nor for one who is strong and healthy." However, if his poverty is not a result of his extravagance and he is unable to earn, then it is permissible to give him zakat. And if you know that he might spend the money on something useless or unlawful, then buy him what he needs and do not give it to him in cash.