We went on a cruise with my fiance's family (dad and stepmom with siblings) for Christmas, where we also got engaged. We had major problems with his step sister. She pretty much ruined the entire week for us, complaining (and getting into fights about) how nobody acknowledged her "engagement" like they did with ours and how everyone likes us more. The whole cruise ended in a blow out, with her calling us fat slobs and scumbags. Her "fiance (they put they were engaged on Facebook but never actually were)" was pounding on our door threatening us. It was a huge mess. She never apologized, and we just completely cut her out of our lives since we got back. My fiance has told his parents numerous times that she isn't invited, and his stepmom insists on bringing their daughter (fiance's niece) with them, which is fine. I could tell they are not happy with his decision, however. When I have mentioned it to other people, they said that it is rude of us not to invite her. My fiance also never got along with his mom, which he also does not want to invite. She has treated him badly growing up, which I can understand. She also got mad she did not know of our engagement before he proposed. I want to leave these decisions up to him, but I am regretful for not including these people and don't want to cause drama with my new family before we even become family. Opinions?