If the perpetual virginity of Mary were just a pious fiction, it would seem that many early churchmen would have rejected these somewhat convoluted explanations. But they did not.
If that were the case they would be stepbrothers.. not half brothers. But they are half brothers because Mary did have other children and it is explicitly mentioned in scripture. The fact that the Roman Church does not want this to be does not change the simple fact that it is.
Even Ignatius, writing to the Apostle John in the first century alludes to the "Venerable James" very Christ like in appearance, as if he were a twin-brother of the same womb.
Hegesippus, a second century Christian Chronicler, writes that James was the Lord's brother, holy from his mother's womb. He calls the grandsons of Jude kindred of the Lord, and says that Jude was the brother of Jesus according to the flesh.
Jesus was a brother to at least six siblings.....four boys mentioned in scripture and at least two sisters, all natural children of Joseph and Mary. Jesus was obviously the eldest.