You offered, “Mary and Joseph had normal sexual relations and Jesus had brothers by blood ...” No, the brothers would be ‘blood brothers’ only if He too derived HIS blood from Joseph and Mary. It is believed in Christianity that JESUS was not a blood descendant of Joseph, and not likely from AMry either. Once implantation in the uterine wall happens, the blood of the gestating child remains separate from the mother’s until the rupture of the amniotic sac at birthing. The newly conceived child builds all of its own structures for life int he water world of the amniotic sac and the body for life in the air world. The mother makes none of the tissues of the gestating child.
Mary’s is the “Seed of the Woman” who crushes the serpent’s head.
Hebrew law states that an adopted child has all the same inheritance rights as a blood born child; God knows what He is doing and He knows what He wrote in the Law and the Prophets about Jesus.
This whole thread is nuts. Jesus had brothers. There is no “permanent virgin zone” for Mary on some supernatural level; else-wise why would Mary have been waiting in the Upper Room for Pentecost to fall, and the Spirit be poured out upon her?
Mary awaited pouring out of God’s spirit as per the Prophet Joel (as Peter quotes) because she was the same as you and me and every other person God chooses out of the world to be His.
I love Catholics but hate all the tacked-on aerie-fairy-Mary-tales.