It's this kind of nonsense that comes out of beliefs based on sola scriptura heresy, imo, taken out of context of the historical, geographic, cultural and lignuistic setting of the Gospels, and misinterpreted in the present-day mindset and New World culture, based on a translation of a translation.
In fact, the Serbian language doesn't even have a word for a "first cousin."
But fortunately for we bible believers, the Greek language knows the difference between a brother and a cousin...And the Apostles knew it as well...
G80
ἀδελφός
adelphos
ad-el-fos'
From G1 (as a connective particle) and δελφύς delphus (the womb); a brother (literally or figuratively) near or remote (much like [H1]): - brother.
G4773
συγγενής
suggenēs
soong-ghen-ace'
From G4862 and G1085; a relative (by blood); by extension a fellow countryman: - cousin, kin (-sfolk, -sman).
Don't you just hate it when the 'Greek proves the bible right???
So much for your history lesson...
Evidently it doesn't know the difference between a nephew and a brother, though, because Abraham calls Lot his "brother" in the Genesis of the Greek Septuagint just like he does in the Hebrew ... but we later find out that Lot is really his brother's son.
And it evidently doesn't know the difference between "brother" and "half-brother," because the Gospels call Philip the Tetrarch Herod's "brother," while secular history records that he was really Herod's half-brother.
And since it doesn't know the difference between brother and half-brother, how do you know that Jesus' "brothers" weren't children of Joseph's from an earlier marriage?*
I mean, until you find that elusive verse that calls them "sons of Mary". You are going to find that verse for us, aren't you?
(*In fact, the parentage of some of Jesus' "brothers" is identified in Scripture for us already. James the Less and Joses are identified as "brothers of the Lord" and their parentage is specified ... and they aren't sons of Mary and Joseph.)
Unfortunately, the Hebrew language doesn't. The word ach (or akh) can mean anything from a brother of the same parents to one of the parents (half brother) to kinship (cousins) and even members of the same tribe.
But, it's not whether a word exists or not that matters onbly, but also what the existing word means (the range of menaings).
The Greek word adelfos (adlephos) can mean brother of the same parents, or one of the parents (half brother), kin, etc.
You will have to find, as Campion points out, an actual biblical refreences that says "Mary's sons" in order to definitively draw a conclusion that she did in fact have other children of her own.