I find it almost impossible to care about this particular topic, and I find it remarkable that anyone spends time thinking about it, John Calvin included.
OK, so why are you in this thread then? Certainly not to attack the teaching, or to lead others away from their beliefs?
Following is a private revelation that erased my last objections to Mary’s perpetual virginity. A little language and culture study helps, and this was revealed to me at a Catholic bible study. In those days, a woman relied on her husband for support. When he died, the children then supported her. If she was childless, she was in dire straights, because she had no one to rely on for support. Even worse, society considered her to be cursed by God, who gave her no children. Such women were shunned, and suffered greatly, reduced to begging for subsistence.
Jesus had great love for widows. This was evidenced by the “widow’s mite” story in both
Luke 21:1-4 and Mark 13:41-44. Christ was so impressed at the widow in the temple that he made a point of teaching His disciples about her selflessness, for the sake of God. Again, Jesus showed His great love for the widow in
Luke 7:11. When He and his entourage met the funeral party leaving the gates of the city of Nain, He took Heavenly pity upon the now childless widow who was enroute to bury her only son. He, as God in Christ, raised her only son to life and presented him to her. God raising an only Son to life. See any similarity?
Then, in
John 19:26-27, Jesus’ last physical act on earth was to give Mary to John, telling him, “This is your mother” and saying to Mary, “This is your son”. Why did He do this at all, and why as He was dying on the cross? If Mary had any other children, they would have supported her for the remainder of her life - especially James, “the brother of the Lord” IF he was the second son of Mary. For Jesus to do this would have been a great insult and disrespect to Mary’s other children, IF SHE HAD ANY. There’s the rub! She had no other children to support her, as John “took her into his home from that hour”
As well, Jesus said “I will not leave you orphans” and neither would He leave His mother a widow without support. Does not the same principle that applies to the Apostles also apply to His own chosen mother?
Again, in the Aramaic, there was no word for “cousin”. So, “brother” and “sister” were used to describe various relatives. Remember that in some cultures, to this day, brother and sister can be used to address even those from the same town or village.
I do not expect this to sway you in your thinking, but it erased my doubt.