Tom:
I agree, this is one of our stock answers to the “brethren” it would applied to step brothers as well as biological brothers.
I don’t mean to use this to cast doubt on the Proto of James, there are many ways children could have been considered the “sons and daughters” of Joseph as written in the proto, and yet not have been biological sons. Let’s not even start to count the possible ways. As I recall from ancient Aramaic the term for “brethren” there were some 30 or so spellings, all meaning basically the same, kin. Not necessarily brother or sister, just “kin”. The word (in the poorest translation possible) was D’aAKHaA, as in † Yukhanan — 12:47
† Acts — 11:29, 12:12, 16:30
† Romans — 8:29
† Philippians — 1:14
† Colossians — 4:15
† 1Thessalonians — 4:9
† Hebrews — 13:1.
OaAKHaA, as in † Marqus — 10:30
† Acts — 15:23
† Romans — 11:14
† 2Timothy — 4:21
LaAKHaA, as in † Acts — 14:2, 15:1, 15:32, 15:36, 16:40, 18:18, 21:7
† 2Corinthians — 9:3, 12:18
(just a few of the 30some spellings, all basically meaning the same.) It’s kind of like saying “aha!” with a cough… LOL, some of the spellings use a DH, or AK, as the first letters. Caution must be used; we’re dealing with a language, which does not have the same alphabet as English.
The words Scripture use to describe the brethren of Jesus mean (in ancient Aramaic) kin, relations.
They may be brothers; they may be cousins, same word. For example if Jesus were to call John the Baptist, He would refer to John as His “D’aAKHaA “ (His cousin), the same word Simon would have used for his biological “brother” Andrew. If they needed to describe the relationship they would trace thru the fathers family, Simon, Bar-Jona (son of John). Enough trivia for the night.