ANSWER: The Papists, in their attempt to prove the perpetual virginity of Mary, insist that "brother" means cousin, and that "firstborn" in Matt. 1:25 is a spurious reading. Dean Alford well says: "No one would ever have thought of interpreting this verse any otherwise than its prima facie meaning, except to force it into accordance with a preconceived notion of the perpetual virginity of Mary." Other Romanists, finding it very difficult to prove that the brothers and sisters are cousins, try to prove that they are Joseph's children by a former marriage!
— Steele's Answers pp. 249, 250.