Help with my little brother

[HitHard69]

Ok, a little background first.
My parents split up a year ago. I'm 20, my bro is 17. I live with our dad, he lives with our mom. We see each other fairly often, but have a pretty rocky relationship. My brother and my dad don't get along well.... As hard as my dad tries, my brother won't forgive him for moving out.

My dad is going out of town on business for 2 weeks and my brother thinks he's having a party while our dad's gone. My dad and I live in a 2 bedroom appt with not alot of space, and my bro plans on having 15-20 kids over to get hammered. I don't want this to happen for many reasons.
1. I live here. I don't wanna have to deal with a HS party. You know how these things are... once word gets out everyone wants to come.
2. He's plays HS football at a school with a very strict athletic code. No drinking, period. I wouldn't have a problem with this BUT this is where I went to school and I'm a coach there now for the freshman team.
3. I don't want to have to deal with a bunch of drunken 16-17 year olds who can't handle thier booze.

I've tried explaining to him that he doesn't live here and he can't just come over and throw a party here. His answer was "Dad gave me a key and said I'm welcome anytime I want."
What's my play here? Basically this kid is accustomed to getting everything he wants, and I have a feeling if I don't let him have people over, our relationship will probably go to hell. He tends to get pissed at me over really small things and stay mad for days. Something like this would probably put me on his shitlist for quite a while.

EDIT TO ADD... He plans on doing it this Friday, and I work untill midnight