'Brother' in the Bible

Paul, called as an apostle (special messenger, personally chosen representative) of Jesus Christ by the will of God, and our brother Sosthenes,

But actually, I have written to you not to associate with any so-called [Christian] brother if he is sexually immoral or greedy, or is an idolater [devoted to anything that takes the place of God], or is a reviler [who insults or slanders or otherwise verbally abuses others], or is a drunkard or a swindler—you must not so much as eat with such a person.

Does any one of you, when he has a complaint (civil dispute) with another [believer], dare to go to law before unrighteous men (non-believers) instead of [placing the issue] before the saints (God’s people)?

but instead, brother goes to law against brother, and that before [judges who are] unbelievers?

To the rest I declare—I, not the Lord [since Jesus did not discuss this]—that if any [believing] brother has a wife who does not believe [in Christ], and she consents to live with him, he must not leave her.

But if the unbelieving partner leaves, let him leave. In such cases the [remaining] brother or sister is not [spiritually or morally] bound. But God has called us to peace.

For through your knowledge (spiritual maturity) this weak man is ruined [that is, he suffers in his spiritual life], the brother for whom Christ died.

Therefore, if [my eating a certain] food causes my brother to stumble (sin), I will not eat [such] meat ever again, so that I will not cause my brother to stumble.

As for our brother Apollos, I have strongly encouraged him to visit you with the other brothers. It was not at all his desire to come now, but he will come when he has the opportunity.