Is a brother considered eligible for Zakat if he possesses gold savings that cover the costs of marriage, and is it permissible for the intention of giving money as Zakat to be a prior intention that it is a gift, and if he is not eligible, then it is a charity?

There is no objection to paying Zakat to a poor brother who does not have enough to meet his needs and does not have enough to marry if he needs to marry. There is no need to inform him that it is Zakat. If the brother owns gold sufficient for his needs and marriage expenses, he is not eligible for Zakat. If you paid Zakat to him knowing that he owned gold, you must pay Zakat again. However, if you learned of this after paying, there is a difference of opinion among scholars; some believe it is not valid and must be repeated, while others believe it is valid. The preponderant opinion is the obligation to pay Zakat a second time to its rightful recipients, because it is generally expected that the brother's financial situation would not be unknown to the Zakat payer.