I think it is curious that the actual question is being avoided here. It is far from a "silly premise" since the question of Mary having other children after Jesus is NOT settled - even to this day. It isn't a black or white conclusion and, instead, has many Biblical evidences for the affirmative. Those who refuse to consider the possibility do so because it WILL affect their ultimate view of the mother of Jesus. That was the point of my hypothetical. You have answered it whether you know it or not. Thank you.
Perhaps I was unclear. The “silly premise” to which I referred is the contention that it could be “shown” - that is, proved by scientific experiment or incontestible historical data - whether Mary gave birth to children other than Jesus.
I’m sure you realize that the references to Jesus’s “brothers and sisters” in the Gospel do not name the parents of those people, and so the only obvious historical source provides no information on the question.