If you actually tell your sister you got those kinds of hickeys and the Duke and crown prince are a pain in ass then she will in a second will help you consulting is the best thing to do
At first I thought the Duke was okay but na bro is trying to rape him and shows that he somehow belongs to him let me tell you something people are way far more expensive than that you can't just be like oh I helped you and now in return you will be my slave or whatever