Why didn't the Apostle John call Jesus's 'brothers' cousins if they were only cousins?
Robert Sungenis answers that Hebrew, with only about 8,000 words, had no word for cousin, uncle or aunt, so relatives were called brothers, and John wrote his Gospel in that Hebrew idiom. He notes that Luke, an educated Gentile with a larger Greek vocabulary, wrote differently, so John's use of "brothers" does not mean Jesus had siblings.
A viewer asks why John did not use the Greek word for cousin to describe the brothers and sisters of Jesus if they were not His actual siblings, a common objection against the perpetual virginity of Mary.
Answer
That is because Hebrew did not have a word for cousin, and John, being of Hebrew extraction, did not even know that Greek had one. Hebrew had a very limited vocabulary of about 8,000 words, with no separate words for uncle, aunt, or cousin; everybody was a brother. John knew Jewish idioms and Jewish vocabulary and that was it, at least when he wrote his Gospel; only later, when he wrote the Apocalypse in the 80s and 90s, did he have a grasp of more sophisticated Greek. Luke, on the other hand, was an educated Gentile, a doctor, very familiar with Greek, and he uses more sophisticated language because he had a much bigger vocabulary and did not come from that Hebrew milieu. So John's use of 'brother' for Jesus's relatives simply reflects the Hebrew way of speaking, not a claim that they were siblings.