Good 4 player co-op games Xbox 360?

I have 3 younger brothers and its easiest to play games when we are all playing together, preferably on the same team. Some games we enjoy are sports games such as FIFA, NBA, Madden, etc. and Marvel Ultimate Alliance 2. I am 20 and wouldn't mind a good co-op team shooting game or something but my brothers range in age from 13-16 and their mom is super anal about them getting M games though they've seen plenty of rated R movies. I would prefer a game where all 4 can play locally or if someone knows of a site or something where you can get 2 games at a discount so we can play LAN that would work as well. I am open to M rated game as long as there isn't nudity or anything too graphic as I may be able to talk my Dad into letting them get it. It seems that good 4 player co-op games are really lacking on the 360. Also we can get a retail or XBLA game. Thanks for any suggestions.