brother, brothers

Definition:

The term "brother" usually refers to a male person who shares at least one biological parent with another person.

In the Old Testament, the term "brothers" is also used as a general reference to relatives, such as members of the same tribe, clan, or people group.
In the New Testament, the apostles often used "brothers" to refer to fellow Christians, including both men and women, since all believers in Christ are members of one spiritual family, with God as their heavenly Father.
A few times in the New Testament, the apostles used the term "sister" when referring specifically to a fellow Christian who was a woman, or to emphasize that both men and women are being included. For example, James emphasizes that he is talking about all believers when he refers to "a brother or sister who is in need of food or clothing."

It is best to translate this term with the literal word that is used in the target language to refer to a natural or biological brother, unless this would give wrong meaning.
In the Old Testament especially, when "brothers" is used very generally to refer to members of the same family, clan, or people group, possible translations could include "relatives" or "clan members" or "fellow Israelites."
In the context of referring to a fellow believer in Christ, this term could be translated as "brother in Christ" or "spiritual brother."
If both males and females are being referred to and "brother" would give a wrong meaning, then a more general kinship term could be used that would include both males and females.
Other ways to translate this term so that it refers to both male and female believers could be "fellow believers" or "Christian brothers and sisters."
Make sure to check the context to determine whether only men are being referred to, or whether both men and women are included.

Strong's: H251, H252, H264, H1730, H2992, H2993, H2994, H7453, G80, G81, G2385, G2455, G2500, G4613, G5360, G5569