Is it permissible to give Zakat al-Mal (obligatory charity) to a friend in need who will spend part of it on legitimate necessities such as housing rent and wedding attire, even though he incurred debt for an extravagant wedding celebration due to his wife's family?

If a person possesses wealth that they squander extravagantly, they are neither poor nor needy, and thus should not be given Zakat. The purpose of Zakat is to fulfill the needs of the poor, not to aid those who are extravagant. However, if their income is insufficient to cover the costs of marriage and housing, and they are in hardship, then they may be given Zakat to complete their needs. You do not have the right to stipulate to the recipient of Zakat that they must spend it on a specific item, for whoever receives Zakat on account of poverty owns it and may dispose of it as they wish, just like the rest of their wealth.