I think I hate my boyfriend’s sister.

I (24 F) have been dating by boyfriend(25 M) for a little over 4 years. All is well and we have little to no problems. But his family can be a bit much. His parents live out of state while his two siblings have moved out of state (From Alaska) but into the same one(Arizona). My boyfriend’s parents loved the idea of having their kids in one space, I’d never moved away, so it made sense. All has been well for the most part. Sister is stressful, domineering, and generally not fun to be around. I am in a safe space with my partner, I adore his brother and his gf who live in the space. It is just the sister who makes everything uncomfortable. She is the oldest, has the most intense rules, is the most favored (ie. going on extravagant trips w parents that other siblings are not informed of, and much more. I have recently moved into this home and for the general part it has been okay, but so many things are expected of us, only of her. I don’t want to give too much detail but I guess am I the asshole. I will clear up any questions in pm.