Yes, I know Xan and Branwen were characters in the first Baldur's Gate, not in Baldur's Gate II. However, they appear in the tutorial, and I know of a couple of cheesy and cheatish ways to get them into real areas.

So naturally I started wondering if there was a more legitimate way to get them in the game, say if someone made a mod at some point or some such. (I just find Xan's outlook entertaining.) Since they have records and a few sounds in the tutorial, I thought that might suggest their files (or partial files) are floating around somewhere in the Baldur's Gate II data (though I have little knowledge of how such things work).

The closest I ever got was converting Xan's sound set from BG1 to BG2, then creating a PC Wild Mage and giving him Xan's voice. That was fun :D

Isn't there a mod around that can include Branwen into the game?

Hmm, I've looked around and found a mod that puts Xan in the City Gates district for you to encounter. It has very poor spelling and grammar in the banters, though, and starts him with a sword of ultimate cheesiness. Oh well, it's not too imperative that I have him - maybe someone will make another Xan mod some day.