I read Gentlemen's Alliance Cross a while ago and I remember being exceedingly confused about the familial relationships between the characters. I know the main character (Haine) is not related to the people she's living with, and that there was something really weird there, and that the emperor of the school was actually his brother, but then he wasn't, or something like that. Can someone explain those two sets of relationships (Haine with her parents and the emperor with his brother/family)?
Haine was born into the Kamiya family, but "sold" to the Otomiya family in exchange for 50 million yen, hence why her family name is Otomiya.
Shizumasa is the emperor, but we first meet the "fake" Shizumasa, who is filling in for the real one, and we find out the fake is actually Shizumasa's twin brother.
For more details including family tree diagrams, see the GAC wikia: