Is OTHER wrong in the post ? POST : A little bit of background...

I have an older sister who is married. The two of them, my parents, and my fiancé and I all live relatively close to each other. My parents have a bad habit of treating my sister differently than they treat me (taking her to dinners, buying her a car, etc) despite the both of us being responsible and financially independent. I am used to this and have been trying to deal with it. 

Tonight was a little beyond what I am used to because it has extended beyond just me. My dad, fiancé, and brother in law all work in the tech world. My dad only invited my brother in law to a holiday party that I know my fiancé would have loved to go to. I am so annoyed that the favoritism has grown to this point....AMTI for being annoyed? Do I have a right to be upset? Should I bring it up to my parents? Nothing has changed the last times I’ve tried to have an honest conversation about how they treat me...