The conundrum that has been set forth in front of you is a difficult one. Your father and brother's brusque abomination of this man's debauchery towards you is understandable. I would listen to their advise for they care about you and are only trying to expurgate this man that they don't feel is right for you. It does not seem that they are trying to churlishly abase your judgement, it simply sounds like they are caring for your well being. Falling in love with a prince seems glamorous, but in reality he won't have any time for you when his state needs him. His ephemeral love for you will be quite the anomaly of what you would expect from true love.