you cannot prove that -all- of jesus' brothers are mentioned by name elsewhere...matthew 12:46-47 and mark 3:31-32 and luke 8:19-20 and john 2:12 and acts 1:14 could easily include brothers of jesus that were -not- mentioned by name elsewhere...
this is basic logic...
Actually, I'm
glad you brought up
Acts 1:14. What is the Greek word used here? It's
ADELPHOI (brothers).
Now, go to
verse 15. What is the Greek word used here? It's
ADELPHOI (brothers). It speaks of
120 ADELPHOI. Are
all of these men uterine brothers?
NO.
We know this because all of the Apostles were there and they
weren't all uterine siblings.
As a matter of fact, of the over
300 times in the New Testament that this word (and variations of it) is used - a whopping
74% of the time, it is
not speaking of
uterine siblings. It is speaking of
cousins, in-laws, uncles, nephews, friends, neighbors, fellow believers, etc.
How can you be certain that these "
brethren" of the Lord were
uterine siblings. You
can't.
Here is
another problem for you. When Jesus was on the cross, He left His Mother in the care of John the Apostle. This would have been a scandal of
HUGE proportions within the family because the
next eldest sibling would have had the task of taking care of her -
not John.
John was chosen because Mary was
ALONE.