Is it permissible to pay off my brother’s debts from zakat funds, and is it permissible for one of them to pay off the other’s debt so that both their debts are cleared, and is it considered a sin to delay paying zakat to one of his friends if he requests that?

The Almighty God outlined the categories for zakat expenditure in Surah At-Tawbah/60, among them being the gharimun (debtors) who are unable to repay their debts. If the debtor is a relative, giving charity to them is better and carries greater reward. It is impermissible to waive a debt owed by someone in hardship and count it as zakat, nor is it permissible to give them zakat on the condition that they use it to repay the debt, or to collude in such an arrangement, even if the condition is not explicitly stated, as long as the intention is to recover the debt. It is permissible to give zakat to a debtor to help them repay their debt without the intention of recovering one's own debt. Delaying zakat for more than a short period (such as two months) is not permissible. It is permissible to give zakat to the gharim so they can pay their debt themselves, or to pay it directly to their creditor. The best approach is to give it to a trustworthy gharim who is keen on fulfilling their obligation; however, if there is a fear that they might misuse it, it should be paid directly to the creditor.