Wendersnaven.com (a resource for nwn2 builders)

Kid Gloves asked a great question on the official forums about cutscenes and multiplayer. Nimdolf gave this answer:

Well after playing the OC with my friend online, it works like this. Whoever triggers the cutscene gets to control it, pick what to say, etc. and all of the other players see the cutscene also and what choices you choose. If you join the game midway through a cutscene however you must wait until it is over to do anything.

Check out the thread:
http://nwn2forums.bioware.com/forums/viewtopic.html?topic=521668&forum=114