Mary did not conceive any more children with Joseph.
Though very rare it's still very plausible looking at it through biblical analysis.
I'm catholic, so I'll have a bias, got to give you that.
Mary was conceived by the Holy Spirit (why we call her the spiritual bride of God) around the age of 12-13, and gave birth to Jesus around 13-14 (estimates are between 12-15 but let's take 14 as a nice number).
Now let's go all through the four gospels, and we'll notice something odd; Joseph gets rarely mentioned and not anymore midway into any gospel.
This combined with Christ giving His mother in care to one of His apostles, we can safely assume that he died rather soon.
The significance of this is that Joseph was already very old when he was appointed as Mary's husband.
Let's go back a bit to Jesus being a 12yo boy who went to the elders in the temple to discuss Scripture (this is the latest that Joseph gets mentioned by his name in any gospel by the way).
Mary could not have safe sex for lets say 3 weeks and not be ovulating for (give or take a week) 2 months after giving birth to Jesus, but after that she should've been good to go in a biological sense (though childbirth is kind of risky under 16).
However, no mention of any other children were made when they returned to the temple in Jerusalem, while in 12 years time they should've gotten at least 2 other kids, both younger than 12.
We can now go all the way forward again to Christ hanging at the cross.
Christ, before He died, said to Mary: "Women, behold your son!" and directly after said to His disciple "Behold your mother!".
Here we see Jesus give a command to His mother.
On its own this would be scandalous to begin with, a son commanding his mother, but Christ was sinless so this could not be the case.
The only explanation would be that the patriarch of the family (the oldest male) was at that moment Jesus.
So, we can now conclude that Joseph was really dead when Christ died on the cross.
What rests are His plausible brothers and/or sisters.
Christ having blood brothers and/or sisters is also disproved with this verse because Mary would not have needed a new son to care for her if she still had living ones.
Thus we have a few possibilities;
- Mary had only daughters after Jesus
- Mary had sons/daughters after Jesus, but all the sons died before Jesus died, thus leaving her without a man to care for her
- Mary was infertile after Jesus and could not conceive a child with Joseph
- Mary stayed a virgin
I, as a catholic, believe that Joseph who knew about the special circumstances of how Mary got Jesus, who Jesus actually was and considering his relative old age for that time (at least 20 years older than Mary, about halfway through an average peasant male's life in 0 AD) did not consume his marriage with Mary.
In all honesty it's all of the above I explained combined with Holy Tradition where we can see that it was agreed upon that Mary did not bear any more children after Jesus.