Looking for a coop game for 3

I'm looking for a Coop game for 3, myself, and my two siblings.

This is where things get fun, the game can be rated M, but can't just have constant profanity. (Little Sister)

The game needs to have guns, swords, bows, and magic won't cut it. (Little Sister)

The game can't be a sandbox type like Minecraft. (Brother)

The game needs to run on older hardware, so nothing new.

(We tried Borderlands, but it was too laggy.)

The current game we are playing is Battlefield 2, any suggestions?

No Magic..... Why ? :(

I wanted to reccomend Trine.... Its got co-op for exactly 3 people. Theres a Wizard who specializes in Magic.... Levitation and Conjuringing.

How old of hardware are we talking? And when you say coop do you mean on ONE screen? I'm assuming not. Also, what age bracket? The old Rainbow Six games for PC are STILL the best in the series and really promote strategy--approaching a scenerio with different people in different positions. ...I don't remember if its coop, but I believe it is.

EDIT: Yeah apparently 8 player max coop.

RAINBOW SIX 3: Raven Shield (though there are three games in the series I believe, and a bundle called "gold edition")

Serious Sam series

Earth defence force

Running with rifles

Shadow grounds

Alien Swarm

Sniper Elite Nazi zombie army

I'll bring Trine up, but arguing with a little sister is hard.

Not super old, but two of our machines are laptops, which puts a damper on things,

I will definitely try Rainbow Six.

I tried earth defense, fun but corny, and apparently my sister prefers shooting humans to bugs, and I'm still not sure how I fell about that. I've never heard of a couple of those, so thanks for the list.

Sanctum 2

Syndicate

Gears of War 3