Advice on Moh/bridesmaid

So, my fiancé and his step-sister have been in my life for about 12 years now. Ever since my fiancé and I got together, his family has hated me for some reason. They told my fiancé we aren't going to last, they told him they like me...but they like me better without him in my life. They have told him I am only with him for his money, which makes no sense. When he called and told his dad he was going to buy a ring to propose to me, his dad said, "Well, I probably won't get to come to this wedding, so I hope I will make it for the next wedding." Insinuating we are not gonna last, and he will get married again. His step sister got mad when I did not text her, immediately, after the proposal. My fiancé changed the relationship status to "Engaged" on Facebook, and it somehow changed mine, as well (We were on a cruise, and my phone just would not work!). She told me I was a horrible friend for not telling her, and she got extremely mad at me for that. She told my fiancé he is dead to her now, but still acting like she cares about him. My fiancé is, actually, in the Air Force, and he is away this year in South Korea. His family has not text me at all asking how I am or if I need anything. They did not even text me to say anything about the Save the Dates that I made, but my fiancé's mother text him about them. They never ask about me or anything. So, even though I have known this family for 12 years, I have pulled away from them because they treat me as if I do not exist. They never make me feel welcomed in their home, it has just been a bad past year being around them. His step-sister was supposed to be my MOH; however, I do not, personally, feel she deserves the right to be in the wedding. She never congratulated me for getting engaged. She never asked to see the engagement photos. She just has not been there for me. Should I, still, make her my MOH? Am I overreacting? I am terrified his family is going to cause issues with everything, and I constantly find myself crying over all of this!