On an purely intellectual level, none of it makes sense. Mysteries of Faith are called mysteries for a reason. How would any of us react if an Angel of God appeared to us and told us these things? How would any of us feel if we were holding an Infant in our arms knowing that He was God? Why would St. Joseph and the Virgin Mary even consider having other children when their Child was THE MOST IMPORTANT PERSON WHO WILL EVER LIVE? Would it have been fair to bring other children into the world, when serving their Firstborn was THEIR SOLE PURPOSE IN LIFE?
Faith is "hope of things unseen" as the Apostle says. Mysteries are not ours to explain or to decipher. If one read everything literally, then a lot of things in the Bible don't make much sense.
Why would St. Joseph and the Virgin Mary even consider having other children when their Child was THE MOST IMPORTANT PERSON WHO WILL EVER LIVE?
You are preaching to the choir, dear friend. Apparently our me-me-me egalitarian bible-only Christians feel that even the Lord wasn't the Alpha and Omega of anyone's life, even of His Parents, and that they would have stopped being intoxicated with love for their awesome Gift and considered other pleasures. How typically fallen!