The gospels name four brothers of Jesus, James, Joses, Judas and Simon, and mention sisters without naming them. James is a substantial figure in the early church, leading the Jerusalem community, and Paul calls him the brother of the Lord in a letter written within a few decades of the events. Any account of perpetual virginity has to say what those texts are describing.
Three answers have been given and each has a name. The Helvidian reading takes them as later children of Mary and Joseph. The Epiphanian reading takes them as children of Joseph by a previous marriage, which is the position of the Eastern churches and the one the Protevangelium supports. The Hieronymian reading, Jerome own, takes them as cousins, on the argument that the Greek word for brother renders a Semitic term with a wider range. The Greek of the gospels has a specific word for cousin and does not use it here, which is the standing objection to Jerome.
The fault line is not where a reader might expect. Luther, Calvin and Zwingli all held the perpetual virginity, and Luther defended it explicitly. Its rejection is a later Protestant development, spreading from the eighteenth and nineteenth centuries as the plain sense of the brother texts came to be preferred over the tradition. So the disagreement runs between periods more than between the Reformation and Rome.