Well, if it's just gonna be you three it's totally fine to just have one set up. Just saying that I have two PS3s and two TVs, so if someone wanted to bring a second PS3 copy or just an XBox with second copy that would be fine too.
Of course, anyone else who wants to come over is more than welcome as well. Just be aware that I only have the two televisions and we can't be playing TOO late since my room mate likes to hit the hay early.