Your fairy tale is based on assumptions you've made, too. No where in the Bible does it mention that Mary had other children. You are assuming it because you see the brothers and sisters of Jesus mentioned in the gospels. As I explained in other posts, the original language (at first I thought Aramaic, but perhaps as someone else mentioned, it was the Greek) does not have a separate term for first cousins or step-siblings, so it is translated as "brothers" although the actual blood relationship may be different. They were probably close family members of Jesus who were raised together. Don't forget that in the Hebrew religion, if a man died, his own brothers were designated to care for the widow and children.
Another reason that points to the idea that Jesus did not have any blood relatives other than Mary was that at His death, He gives John the responsiblity of looking after His mother, Mary. If Jesus had other brothers and sisters, as you say, then this would not have been necessary. Jesus as Mary's son had to designate someone to take care of her. If she had other children, Jesus, again, would not have done this. There would have been no need.