Name of book?

Need help remembering name of book, this is what I remember: At a university FMC is/was an assassin One of the MMC is also an assassin (in charge of other assassins) When first starts at the school, she has to touch a spear to determine which group she is supposed to join people think she’s spoiled at first, but she’s not One of the MMC has wings and another has a tail (they are brothers I think) I think they have to go through some kind of trial or competition while at the school, and there’s an oracle who ends up being sent on the trial with them I believe