Too often we think first of Cain and Abel when we think of biblical brothers. There are other examples of discord between Esau and Jacob, but they were reconciled, and we don’t teach of that often enough.
Jacob feared their meeting, made preparations for a battle, then when he saw Esau coming, separated his children:
And Jacob lifted up his eyes, and looked, and, behold, Esau came, and with him four hundred men. And he divided the children unto Leah, and unto Rachel, and unto the two handmaids. (Genesis 33:1 KJV)
He need not have been concerned.
And Esau ran to meet him, and embraced him, and fell on his neck, and kissed him: and they wept. (Genesis 33:4 KJV)
Could two brothers have been closer than Moses and Aaron?
And the LORD said to Aaron, Go into the wilderness to meet Moses. And he went, and met him in the mount of God, and kissed him. (Exodus 4:27 KJV)
How about the love Andrew held for Simon Peter, enough to share what he had learned?
One of the two which heard John speak, and followed him, was Andrew, Simon Peter's brother. He first findeth his own brother Simon, and saith unto him, We have found the Messias, which is, being interpreted, the Christ. (John 1:40-41 KJV)
How much more should we be loving our siblings, when we come to know we are the children of God?
For as many as are led by the Spirit of God, they are the sons of God. For ye have not received the spirit of bondage again to fear; but ye have received the Spirit of adoption, whereby we cry, Abba, Father. (Romans 8:14-15 KJV)
Paul continues that theme in other epistles.
But when the fulness of the time was come, God sent forth his Son, made of a woman, made under the law, To redeem them that were under the law, that we might receive the adoption of sons. And because ye are sons, God hath sent forth the Spirit of his Son into your hearts, crying, Abba, Father. (Galatians 4:4-6 KJV)
Before he did so, Christ made it apparent when He taught us how to pray:
After this manner therefore pray ye: Our Father which art in heaven, Hallowed be thy name. (Matthew 6:9 KJV)
So, how are we to treat our brothers? Rhetorical question. The Bible tell us we already know.
But as touching brotherly love ye need not that I write unto you: for ye yourselves are taught of God to love one another. (1 Thessalonians 4:9 KJV)
As the author begins the closing chapter in Hebrews, we are given our final instructions regarding brotherly love:
Let brotherly love continue. (Hebrews 13:1 KJV)
Let us do so, quickly.