Me and my brother have been playing Baldur's Gate 2's multiplayer lately (he almost refuses to play by himself)

But we have not tried Neverwinter Nights yet which I heard is a little more Co-Op oriented, I just want to ask is that true?

Yes. Yes, it is true.

If you haven't yet, I would suggest downloading NWNCX (the Neverwinter Nights Client Extender), version 0.2.7 (or later, if another update is added). It restores functionality to the multiplayer server list that is otherwise blank (since GameSpy stopped supporting NWN).

Even almost 11 years after the game came out, there are still many different servers (and styles of servers) online. I suggest browsing around, checking out their websites, etc. until you find a server or persistent world (PW) that you would enjoy.

Many multiplayer servers for NWN make use of hak files (additional content), so you will likely need to download such files before logging in.

I'm going to put a link here for you: www.neverwinternights.info It's got lots of information and links to more if you have any questions about the game. The forum link on that site leads to the BioWare NWN forum, where you're likely to get answers to questions a bit quicker than you would here. Many of us "regulars" don't visit the gog.com NWN forum often.