This reminds me of Maxwell Smart. The old gun in the hat trick. The until argument has been defeated so many times on this forum. You can believe novel ideas or follow the ECF.
Let's see what St Jerome says
Jerome, cont. Hevlid. 8: Lastly, I would ask, Why then did Joseph abstain at all up to the day of birth? He will surely answer, Because of the Angel’s words, “That which is born in her, &c.” He then who gave so much heed to a vision as not to dare to touch his wife, would he, after he had heard the shepherds, seen the Magi, and known so many miracles, dare to approach the temple of God, the seat of the Holy Ghost, the Mother of his Lord?
Jerome: From the words, “her first-born Son,” some most erroneously suspect that Mary had other sons, saying that first-born can only be said of one that has brethren. But this is the manner of Scripture, to call the first-born not only one who is followed by brethren, but the first-birth of the mother.