Some examples of the term “Brother” used as a title and to refer to brethren in the faith…
Either how canst thou say to thy brother, Brother, let me pull out the mote that is in thine eye, when thou thyself beholdest not the beam that is in thine own eye? Thou hypocrite, cast out first the beam out of thine own eye, and then shalt thou see clearly to pull out the mote that is in thy brother’s eye. Luke 6:42
And Ananias went his way, and entered into the house; and putting his hands on him said, Brother Saul, the Lord, even Jesus, that appeared unto thee in the way as thou camest, hath sent me, that thou mightest receive thy sight, and be filled with the Holy Ghost. Acts 9:17
And when they heard it, they glorified the Lord, and said unto him, Thou seest, brother, how many thousands of Jews there are which believe; and they are all zealous of the law: Acts 21:20
came unto me, and stood, and said unto me, Brother Saul, receive thy sight. And the same hour I looked up upon him. Acts 22:13
Gaius mine host, and of the whole church, saluteth you. Erastus the chamberlain of the city saluteth you, and Quartus a brother. Rom 16:23
Paul, called to be an apostle of Jesus Christ through the will of God, and Sosthenes our brother, 1 Cor 1:1
Paul, an apostle of Jesus Christ by the will of God, and Timothy our brother, unto the church of God which is at Corinth, with all the saints which are in all Achaia: 2 Cor 1:1
And account that the longsuffering of our Lord is salvation; even as our beloved brother Paul also according to the wisdom given unto him hath written unto you; 2 Peter 3:15
Titles such as “Father” and “Master” are forbidden (Mt 23:9). Ministry functions such as apostle were not used as titles (ie: “Paul an apostle” not “the Apostle Paul”). The only valid title we should hope to be known by among fellow believers is “brother” or “sister”.