Author-san has to square out the relationship between the parentals. If it's romantic love (disgusting) dad should be in prison.
Idk how it's gonna play out. A game of house that's filling a hole in the sister one's heart or something that is, for all intents and purposes, malicious. Although it could unintentional but still
Mom/Dad role I could somewhat understand but why onii-san? Are you implying that onee-san can't possibly protect imouto? Or was it (morally) wrong to be siscon/have a crush toward onee-san (but being creepy toward onii-san is fine, apparently)?