Is it permissible to give zakat to a brother to help him with marriage expenses, and is it permissible to leave this money with the father who is responsible for collecting the marriage expenses?

It is permissible to give zakat (definition) to a needy brother according to the majority of scholars, including Abu Hanifa, Malik, and Al-Shafi'i, as well as one of the two narrations from Ahmad. If your brother is needy and cannot afford to get married, it is permissible for you to give him from the zakat what he needs to marry, provided: there is no extravagance, it is done in an appropriate manner, and he fears falling into temptation due to his poverty and his father's inability to marry him off. It is permissible for you to appoint your father to deliver the zakat to your brother, but your obligation is not discharged until the money reaches your brother, unless your father is an agent for your brother in receiving the zakat, in which case your obligation is discharged upon handing it over to your father.