Is it permissible to give zakat money to the husband's brother for the treatment of his son, who has limited income and high medical expenses? And is it preferable to be discreet when giving the money, such as presenting it to his wife without the husband's or his brother's knowledge?

It is permissible to pay zakat (definition) to the husband's brother if he is one of the eight categories deserving of it, such as being poor and unable to meet his needs and the needs of those he supports, including medical expenses, as Allah Almighty says: "Indeed, zakat expenditures are only for the poor and for the needy..." It is also permissible to give zakat to his wife if she will deliver it to him, provided that the zakat enters his possession, as he is the one entitled to it. It is not necessary to inform him that it is zakat unless he is someone who does not accept zakat. If the money belongs to the wife, she has the right to spend the zakat as she wishes without her husband's knowledge. However, if the money belongs to him, she may not dispose of it without his authorization.