Thread:HazelQuill7445/@comment-26111940-20161031170718/@comment-26111940-20161031175846

I had reasoning behind that, actually. Taiyang would have had to legally adopt Yang, giving her his surname. This is because, at birth, if parents are unmarried, the mother is the only one with legal guardianship as the law sees the father as someone who has not been proven to be related by blood, so they do not share guardianship.

With Jacques Schnee, it's the same thing that happens with the Royal family. People who marry in all become members of the House of Windsor. It sometimes happens with the owners of big businesses.