Is it permissible for the husband to perform the marriage contract (aqd qiran) for his brother, according to Sharia, after the completion of the court procedures, and what is the legitimate صيغة (formula) for that?

For a marriage to be valid, there must be an offer from the guardian, such as him saying: "I marry you to my daughter so-and-so," and an acceptance from the husband, such as him saying: "I accept to marry her," along with the presence of two just witnesses. The presence of a marriage officiant is not required, nor are specific phrases for the formula. The majority of scholars hold that the offer comes from the wife's guardian and the acceptance from the husband. However, according to the Hanbalis, the offer must precede the acceptance. As for the proposed formula, one can begin with the Khutbat al-Hajah (definition) (Sermon of Need), then the guardian states the offer and the husband accepts. It should be noted that most of what is mentioned in this formula is not essential. If the guardian says: "I marry you to so-and-so," and the husband says: "I accept her marriage," in the presence of two just witnesses, the contract is valid.