Anti Catholics think Mary had other sons because they are “unlearned”, having rejected the authoritative teaching of the Church. Thus they “wrest scripture” in this, as in countless other matters, “to their own destruction” (2 Pet 3:16).
That Mary was ever virgin is completely Biblical, and is crystal clear right from the beginning of the New Testament to the very end of Jesus’ life - clear, that is, to those who have eyes to see and ears to hear.
At the Annunciation, Mary asks Gabriel how she will bear a son (“How can this be?”), given that she “knows not man”. Note that she asks this question BEFORE Gabriel announces that her Son will be born of the Holy Spirit. The exact sequence of the conversation is most important, because it unmistakably points to Mary’s vow of perpetual virginity. The question she asks of Gabriel makes no sense WHATSOEVER if Mary was indeed planning to consummate her forthcoming marriage to Joseph - in that case, the ONLY logical and natural conclusion she (or anyone else in her place) would have drawn from Gabriel’s words was that he was speaking about a child which she would bear (“You will bear a son…”) from a conjugal relationship with Joseph.
Then, at the end of His life, from the Cross, Jesus gives His Blessed Mother to St John - who takes her into his home. Now in Judaism, great respect was given, concern was shown, and indeed provision made in the Law (Torah), for widows. (We have to assume Mary was by the time of Jesus’ death a widow - or she’d have simply gone home to her husband Joseph after Jesus’ crucifixion). But no, she goes to live with St John. In Judaism it would be a publicly scandalous disgrace if a son or daughter refused to take in a widowed mother to live with him/her. If Jesus had, as is alleged, brothers (plural!) and sisters (plural!) why didn’t Mary go to live with even a single one of them? Did they all refuse to take her in? Had Mary and Joseph raised such disgraceful children, who were either totally ignorant or uncaring about their Jewish traditions? Did Jesus come from a family of bad stock? Did Jesus’ holiness and His teachings have no effect on His own siblings? Puh-leeze! So many of these “non Catholic Christian” doctrines/beliefs seem designed to ultimately belittle/diminish the respectability, holiness, power or glory of Christ! I’m not kidding - I could list scores of them and point out what the diabolic/blasphemous suggestions/conclusions underlying each of those doctrines are… but that would be off topic here.
Of Mary’s sinlessness, St Augustine wrote: “Every personal sin must be excluded from the Blessed Virgin Mary for the sake of the honor of God.”
In the same vein, one must conclude that for the sake of the uniqueness and dignity of Mary’s womb - which was the truest, holiest tabernacle there ever was - all other content or fruit (other than the incarnate Son of God) must be excluded from it. Indeed, from Old Testament times Ezekiel prophesies Mary’s perpetual virginity when he says: *And the Lord said to me, “This gate shall remain shut; it shall not be opened, and no one shall enter by it, for the Lord, the God of Israel, has entered by it. Therefore it shall remain shut. * There is no other gate that Jesus (the “Lord, the God of Israel”) entered the world through but the womb of Mary - and it was “shut” thereafter, exactly as prophesied. Mary remained a virgin before, during and after the birth of Jesus.
Mary is the prototype of the Church. She was ever immaculate (sinless), otherwise the Church could not be the spotless Bride of Christ. Mary was also ever-virgin, otherwise the Church would be enjoined also to another besides Christ. (And outside of Christ, there is only one other - one who is forever attempting to dispute and distort the glorious Truth which Christ has revealed to His one true Church).