[conservonator]

AFAIK, Roman Catholic interpretations have never insisted that Mary was perpetually virgin. Never the less, the other offspring of Mary would be half-siblings at best in the eyes of the Catholic church.

Both the Roman Catholic and Orthodox Churches hold the belief in the perpetual virginity of the Blessed Mother.

[B Knotts]

I would add that, as far as I know, the various other particular churches (such as the Coptic Church) hold the same belief in the perpetual virginity of Our Lady.

So, that's around 1.7 billion for; 350 million against.