Why does my family adore my sister and her rude boyfriend?

[Johanna]

My sister is 21, her boyfriend is mean, arrogant, and a jerk. She used to be very independent. Sometimes she's pushy, mean, arrogant, and fussy. She thinks she looks great in everything and acts like she is better than me and everyone else. My mom talks smack about her behind her back about how she never calls or visits and has all these excuses about why she never visits. And when she is not around my mom is not mean to me. But when my sister comes around, she flips immediately and treats her fine, doesn't act like she's mad anymore, and at times is very mean to me. Other members of my family feel the same my aunts and uncles think she is just the best. I'm not mean, i'm not "two-faced", I'm funny and normal. She hasn't done much with her life, and they adore her and her boyfriend(who we suspect could be abusive) everyone says they hate him, but when he comes around they act like nothing happened. Why do they love them so much and not us (me and my BF)? Whats goin on-I'm confused!?