It doesn’t sound like you addressed the direct answer to what was asked concerning the Apostle John at the foot of the cross.
This also is only opinion, even if one states they have no doubt Mary and Joseph had a large family after Jesus was born.
So, Orthodox and Roman Catholic faiths do not see it per the questions of children of Joseph and Mary and have thought that for 2000 years, they were much closer to the situation but somehow, one asserts they know in the present day and 2 or 3 continents away?
This is, to be brief, just apologetics. Questions asked many times already.
From Catholic Answers, this deals with the Greek word “Adelphos” which can mean cousin, nephew, etc.
“The Bible is simply silent on the exact relationship between Jesus and the other two men, Simon and Jude, mentioned in Matthew 13. This proves two important things. First, it proves that the Greek word for brother is sometimes used to mean something other than sibling, and it proves that Matthew 13:55-56 in no way demonstrates that Mary had other children.”
And on perpetual virginity:
In the end, at least, per did Mary bear other children, I don’t think a clear answer is given, yes or no.
1 Corinthians 15: 6, Paul says “500 Brothers” saw Jesus appear, so are we to think these are all blood brothers? Of course not.