I feel like a bad person.

My boyfriend of 1 year is very close with his family. We go to his parents house maybe 3 times a week. His sisters are 11 and 4. The 11 year old literally drives me insane. She screams everything she says, she repeats everything until you aknowledge she's talking, she says things that are so obvious and keeps saying them. It's so obnoxious. She always has to be right even when she's wrong and I'll correct her she'd just go "uh no you're wrong". I love the 4 year old so much she's like my own sister, but the oldest drives me up the freaking wall. I don't like loud crazy obnoxious know-it-alls. I feel terrible because I know she's just a kid but I completely disagree with the way they are being raised. They are so incredibly spoiled it makes me sick. How do I deal with this? Is this normal? I want kids one day (I'm 19 SO is 24) but if I can't handle an 11 year old should I? Please I need some advice. Have you had this happen to you? I can't ever say anything because he's so protective over them and thinks I'm being mean.