But the New Testament is not part of the Septuagint, nor were St. Elizabeth and the Blessed Virgin brothers.
To expand:
Koine and classical Greek did have words to suggest the relationship of cousin-german—”anepsios”—and broader, non-specific kinship—”suggenes.” But neither was preferred to adelphoi in referring to legal sons of the same father.
Greek did not distinguish between stepsons and blood brothers at that time and today uses the word “progonos,” which in koine times meant only “elders” or “ancestors.” Greece and the Middle East at the time were entirely patriarchal; it was the relationship of the children to the father which was determinative. Since Jesus and the brothers were, under the Orthodox thesis, both understand to be fathered by Joseph according to the Law, it was entirely unremarkable that the Gospels made note of Jesus’ adelphoi.
Num 36:11; Tob 7:2, Tbs 9:6 or Col 4:10How about GSN-431