I'm pretty sure you can't log in the same PSN account in multiple locations at the same time, but I might be wrong. In which case, being able to play together won't be possible, especially since you actually need to be signed on to access the internet. It's not much bother making another account though.

It would also mean that, in theory, only 1 person would have to buy the PS3 version of the game and than everyone who wanted to play could then use that 1 account. It just wouldn't work.