...if you're playing in Mom's house, I'm afraid I've gotta back Mom up on this one... Let the lil bro play... keep Mom happy and, in so doing, keep mom's house as a place to play in the future.
Heck, who knows, maybe little brother will play for a while, get terribly bored, and decide he's out before you do... On the other hand, maybe little brother will turn out to be a better player than you or your friends expect (wouldn't that be cool?) and, in retrospect, all of this concern will turn out to have been for nothing. And, you know, even if he doesn't turn out to be the best gamer in the world, it's still an opportunity to take the kid under your wing and help him to learn right?
Honestly, I'd be a little more concerned about your "friends" who are so quick to protest the very thought of your bro playing as I would be your brother. Friendships are often fleeting, you know... Family's forever.
Moved this to the Common Room, btw... Q&A threads are for discussions related to games that are running on the forum... General discussion questions are usually posted in the Common Room.
Aaaaaand... Welcome to the Inn, huh?