Matthew 12:50
For whoever does the will of my Father in heaven is my brother and sister and mother.
As long as referring to Jesus as brother does not indicate some underlying question to his divinity or supremacy. And, it shouldn't...any more than applying the term Son of God questions his identity as the Everlasting Father. The term brother here indicates a comradeship and status as a friend. After all, it was Jesus himself that chose to lower himself to become a man so that he would be a brother to humanity.
What is man, that thou art mindful of him? and the son of man, that thou visitest him?