Matthew 1:25
Matthew 1:2525But he had no union with her until she gave birth to a Son. And he gave Him the name Jesus.
is one of the JW counter-texts against Catholic perpetual virginity of Mary. The Watchtower reads "did not have sexual relations with her until she gave birth to a son" as ruling out the Catholic doctrine — the natural temporal sense of "until" implies that after the birth, normal marital relations resumed. JWs also cite the verse against Mariolatry more broadly. The verse is a place where the JW position and the Protestant position genuinely converge against Rome.
Affirm the common ground with the Witness. Protestants also reject perpetual virginity, the Immaculate Conception, the Assumption, and prayers to Mary. in the NWT matches the natural Greek reading: Joseph "did not have sexual relations with her until she gave birth" — and names Jesus's biological brothers and sisters. Jerome invented the cousins theory in AD 383 in his Against Helvidius specifically to preserve perpetual virginity, and the New Catholic Encyclopedia admits it. On all of this, Protestants agree with the Witness against Rome. The pivot is to ask: "we agree about Mary's other children — can we now look at the Christological question of who her firstborn was?" Pair with (Immanuel = "with us is God") to walk the conversation from common ground on Mary to the question the Watchtower's Mary chapter actually targets — the Incarnation itself.