"This letter is from your brothers, the apostles and elders. We are writing to you Gentile believers in Antioch, Syria, and Cilicia. Greetings to you" or "To our Gentile brothers in Antioch, Syria, and Cilicia. Greetings from the apostles and elders, your brothers"
Here the word "brothers" refers to fellow believers. By using these words, the apostles and elders assure the Gentile believers that they accept them as fellow believers.