Wedding Drama My own cousin is starting to get really vindictive?

I never thought that a joyous occasion would bring out the worst in people. I didn't think that having a wedding would bring out the worst in my friends and family. But it has. I originally was going to have "Sally" my BFF since I was 5 as my Matron of Honor. The she out of the blue started tripping on me stating I never been there for her and blah, blah. This is not true. AT the same time I asked my cousin "Angela" to be my Bridesmaid. I asked both Sally and Angela if it were ok if I give each other's phone number since this was my bridal party. They exchanged but now Sally and I had had a big blowout and we are not friends anylonger, however I seen plastered on FB that she Angela have been boosom buddies and going to concerts and hanging out. What weird is that they didn't even know each other before me. I was ok with it and even considered making my cousin my new MOH, however I got sick and postponed the Wedding from May to Sept because I had surgery. During this time my cousin stated I wasn't telling her anything about the surgery. I explained to her that its something I needed to get done. It was very private and I felt I didbn't have to disclose any info. During this time I text and emailed my cousing just to say hi and she never responded. Then I called her one day and she said, "Oh I was waiting for you to call me!" I'm thinking really? Who do you think you are. But I swore she sounded so much like Sally. Then night of my surgery I called my cousin just to say I made it out the surgery fine she said, "Oh let me call you back I gotta finish cleaning my garage before it rains!" I was done! Here I am calling her and I had the surgery. I started replanning my wedding and I asked my cousin to do a wedding in the ceremony rathan than be in the wedding. And she said she rather not. My MOH is a very good GF that has been there for me throughout this whole painful surgery ordeal and even before. And I asked my SIL to be my Bridesmaid. Two attendants. Real simple. My brother's girlfriend volunteered to help me with decorating and getting party favors. Now fast forward to yesterday. My cousin invites my brother's girlfriend and Sister-in-law to a play. They only met one time at my place for a XMAS party me and Fiance` had. They are a group of 15 girls going. One of whom I'm sure is Sally my ex-bff. My brother's GF and SIL don;t know the whole story about Angela and Sally but I just find it disrespectful and undehanded that my cousin feels she has to befriend these ladies in my life and even more disheartening none of these ladies seem to say"Hey did you see if Jade wanted to go?" I am so angry and I don't understand why these females are so spiteful. Is it jealousy? Is it revenge? Is it to hurt me? Should I even have my brother's gf and sil in the wedding involvement at all. What would you do?