When a mixture of younger close relatives (e.g. half-brothers, cousins, blood brothers, adopted children) is described in one word, the Middle Easterners to this day use “brother” or “sister”. Specific words for “nephew” etc. exist, but it doesn’t mean they are used unless the precise relationship is the focus of the speech.
Even when a single person is referred to, and he is not a brother, the Scripture still uses “brother” at least in one occasion, when Abraham calls Lot his “brother” when in fact we know Lot was his nephew.
In a culture of large extended families sharing the household it is not unreasonable.
At least two of the supposed “brothers” are attributed to Mary Clopas and not to the Blessed Virgin in another gospel.
This does not prove that Mary never had other children. It just shows that the scripture prooftext about the “brothers” isn’t.
How we know that Mary had no other children? We infer it. First, theologically, as the totality of human fulfillment inherent in the choice of being the virginal Mother of God would seem to preclude other familial ambition. If God made a part of your body a holy-of-holies temple, would you fool with it? Second, if Jesus had blood relatives, why would St. John the Evangelist chosen as caretaker? Thirdly, it doesn’t seem that the purpose of the marriage of Mary to Joseph was to make babies anyway. When Archangel announces to Mary, she seems perplexed by the suggestion that she would become pregnant by anyone. “I know not man”, she replies. How many young brides do you know who marvel at the idea that they would soon give birth to a great man? She had never intended to be a mother, or to be a consummated wife.
So your position is that it is not definitive that Jesus had literal brothers and sisters from Mary; He may have, He may not have. The scripture is inconclusive?
How we know that Mary had no other children? We infer it.
And what scripture provides the basis for that inference?
First, theologically, as the totality of human fulfillment inherent in the choice of being the virginal Mother of God would seem to preclude other familial ambition.
That is simply a statement, not a reason. You infer that Mary is virginal because your theological statement says she is virginal.
Second, if Jesus had blood relatives, why would St. John the Evangelist chosen as caretaker?
Why not Joseph's family? Or Mary's sisters, or other relatives? In fact, your own position - they were cousins, not brothers and sisters - would run counter to your own claim that Jesus did not have blood relatives.
Jesus chose John for symbolic reasons, I submit. John was not needed to take care of her physically; John was needed to care for her spiritually. Jesus named them mother and son spiritually, to tend to each others spiritual needs.
Thirdly, it doesn’t seem that the purpose of the marriage of Mary to Joseph was to make babies anyway. When Archangel announces to Mary, she seems perplexed by the suggestion that she would become pregnant by anyone. “I know not man”, she replies. How many young brides do you know who marvel at the idea that they would soon give birth to a great man? She had never intended to be a mother, or to be a consummated wife.
Ummm, Mary and Joseph weren't married when the angel appeared; they were engaged. Mary and Joseph - being good Jews - would not have consummated marriage because they were not yet married. Mary was perplexed because she had not even married, let alone slept with her husband-to-be!