9 year old, 1 am, still up!

Okay, this is ridiculous, but I'm just here to ask if I'm in the wrong? My sister is 9 years old! She has a friend over and it almost one and they are still awake, my mom is out cold, she's pretty much drunk, I keep telling them to go to sleep, well my sister has a bad mouth and is always talking back, and telling me to shut up, and blah blah. So I say keep talking to me and I'll call the dad, my other sister comes out of her room, and tells my sister the exact thing, well she starts crying and tells on me, my sister comes down yelling at me, pretty much threatening me, I'm pregnant my boyfriend says I'm in the wrong, what is it doing that is so important for her to go to sleep? She's 9 years old. She needs to be in bed. I do not feel like I'm in the wrong.  It is a school night!