You’re noble^3, kill your dad(s) and siblings

Hint 1: >!Dad #1 is the reason you have to kill Dad #2!<

Hint 2: >!Your cousin is a romance option, along with your siblings!<

Hint 3: >!You don’t remember Dad #1 even exists, let alone that he’s your dad, until your cousin/possibly wife tells you to go kill him!<