This presumes that there would have been a need to do so. There are a lot of details in the Gospels for which the Evangelists spend no time whatsoever going into further detail about. That's because the Gospels aren't biographies in the modern sense of the term, they are Gospels. The only reason why Jesus' siblings get brought up at all is to establish narrative context for what Jesus said and did.
We should temper our expectations of what information the biblical writers saw fit to mention; they weren't writing with the assumption that two thousand years later we'd be reading these texts and guessing about certain details. They wrote these texts in the particular historical circumstances of their own time, addressing the things they believed necessary for their own purposes. Why doesn't Mark mention Jesus' birth? Well that wasn't part of the story of Jesus that Mark was trying to focus on.
So we should ask: Is there any reason why the Evangelists should need to say whether or not Jesus' siblings were or weren't Mary's children? If these were the children of Mary, and this was known by the Christian communities already, then there's no reason for the Evangelists to bring it up if there's no reason to do so; and conversely, if these were the children of Joseph from a previous marriage, and this was known by the Christian communities already, then there's no reason for the Evangelists to bring it up if there's no reason to do so.
This is all to say that using the silence of the Evangelists as evidence of a particular proposition here requires an a priori assumption of the conclusion: If I already have decided that these are Mary's children, then the silence of the Evangelists just means that we should assume these were Mary's children. If I have already decided that these are the children of Joseph from a previous marriage, then the silence of the Evangelists just means that we should assume these were the children of Joseph from a previous marriage.
So what we are left with is: We don't know. At least not from Scripture alone. Scripture doesn't provide us with these answers. And, since Christians treat the Church's received tradition with varying degrees of deference, the simple antiquity of the tradition provides sufficient support of this view. That is, tradition favors the side that these are not other children of Mary, thus these are not blood-siblings of Jesus at all, but children of Joseph from a previous marriage. Or, alternatively, in the West the view that these were probably cousins gained a great deal of traction.
Is that tradition correct? Well, how we answer that then gets into bigger conversations about things such as tradition and ecclesiology. But it still doesn't really get us any closer to a definite biblical answer to our inquiry, because Scripture still remains quiet on the subject.
-CryptoLutheran