I'm going to kick my brother out of my car
What did your brother do in your car that is causing you to want to kick him out?
I don't want him to fall asleep and spoil my car's leather
Your brother is annoying to you when he falls asleep in your car, that is plain to see. Kicking him out for sleeping is irrational, nothing will be done to your car after someone sleeps on it. You will just gain a brother who hates you for this if you follow through.
Nah I'm still going to kick him out. I have to do this so that no one falls asleep in my car.
It is ultimately your decision to kick him out or not. Just try not to make a bigger deal over the situation than it really is. He is your family nonetheless.