First, show us where in Scripture it is documented that other children, i.e. brothers and sisters of Jesus, were born of the Virgin Mary.
Second, show us where in Scripture the doctrine of Sola Scriptura is specified.
I personally can't document #2, sola scriptura. Others around here seem to be comfortable arguing the point. But I do accept it.
If I don't, I have to determine who is right regarding many extra-scriptural pronouncements. That would give me a colossal headache. (Case in point, do you accept every point that every Pope has claimed as from God? I am assuming you are Catholic.) So I do rely on Scripture alone as my guide. (I will admit, there are so many interpretations of scripture floating around that that in itself is a slippery slope.)
As to point one, while there may be no evidence that Jesus' brothers (and sisters?) were born of Mary, you cannot show me scriptural evidence they were not. The fact that Jesus' family is referenced in Scripture seems to me to be inclusive.
I am not a Catholic, so I do not necessarily accept the Catholic interpretation of God's Word nor its doctrines. But I would never engage in Catholic bashing.