It has to do with inheritance. Only one child can be raised in a mage family, because there is no point in splitting the crest between children and having two less powerful mages when you can have one very powerful mage as your successor. My sister was adopted away to a mage family whose bloodline could no longer produce mages. As the older sister and one who inherited the family name it is imperative that I affirm that I was the right sister to keep.