Includes, besides sons of the same parents, cousins and near relatives, as a nephew (Genesis 13:8; Genesis 14:16; Deuteronomy 25:5-6 margin). One of the same tribe (2 Samuel 19:12). Of the same or a kindred people (Exodus 2:11; Numbers 20:14). A friend (Job 6:15). A fellow man (Leviticus 19:17). "A brother to (i.e. a fellow on a level with) the dragons" or "jackals" (Job 30:29). As the outer pagan world knew believers by the name "Christian," so they know one another by the name "brethren" (Acts 11:26; Acts 26:28; 1 Peter 4:16; compare Matthew 25:40; Acts 11:29). The Jews distinguished a "brother" as an Israelite by birth, and a "neighbor" a proselyte, and allowed neither title to the Gentiles. But Christ applied "brother" to all Christians, and "neighbor" to all the world (1 Corinthians 5:11; Luke 10:29-30). The arguments for the "brethren" of Jesus (James, Joses, Simon, and Judas) mentioned in Matthew 13:56 being literally His brothers, born of Joseph and Mary, are:

(1) their names are always connected with Mary, "His brethren" is the phrase found nine times in the Gospels, once in Acts (Acts 1:14);

(2) nothing is said to imply that the phrase is not to be taken literally. But:

(1) "My brethren" is found in the wide sense (Matthew 28:10; John 20:17).

(2) If Joseph had been their father, they would have been some one time at least designated in the usual mode "sons of Joseph." The statement that. His "brethren did not believe in Him" (John 7:5) may refer to His near relations generally, excepting the two apostles James (who is expressly called "the Lord's brother," Galatians 1:19) and Jude (Judges 1:1). In Acts 1:14 His "brethren," as distinct from the apostles, may refer to Simon and Joses and other near relatives. It is not likely there would be two pairs of brothers named alike, of such eminence; James and Jude. His brethren are, most probably, the writers of the epistles.

(3) It is expressly stated that Mary, wife of Cleophas and sister of the Virgin Mary (John 19:25), had sons, of whom James and Joses are named (Matthew 27:56; Mark 15:40). How unlikely that two mothers of the same name, Mary the Virgin and her sister, should have sons also bearing the same names.

(4) If the Virgin had had sons of her own, Jesus would not have given her in charge to John (John 19:26), who was not a relative.

(5) It is a fitting thing that in Jesus the line of David should have its final consummation. The naming of Jesus' brethren with His virgin mother so often may be because Jesus and she took up their abode at the home of Mary, the Virgin's sister, after Joseph's death; for that he soon died appears from his name being never mentioned after Luke 2. Hence the cousins would grow up as brothers. The very difficulty implies the absence of collusion or mythical origin in the gospel narrative.

"Firstborn son" (Matthew 1:25) does not imply that any sons were born of the Virgin afterwards, but that none were born before Him. Exodus 13:2 defines "the firstborn" "whatsoever openeth the womb": whether other children followed or not. "Knew her not until" does not necessarily imply he even then knew her; compare Genesis 28:15, "I will not leave thee until I have done," not meaning He would leave Jacob even then. The main truth asserted is the virginity of Mary up to Jesus' birth. What was afterward is not dearly revealed, being of less consequence to us.

Bibliography Information
Fausset, Andrew R. Entry for 'Brother'. Fausset's Bible Dictionary. https://www.studylight.org/dictionaries/eng/fbd/b/brother.html. 1949.

Bible Dictionaries Brother

Fausset's Bible Dictionary

Bible Dictionaries
Brother