The first time I encountered this problem was with the “Red Hand Of Doom” campaign released by Wizards a few years ago. When the PC’s arrive to defend the final town, they’re brought before the town’s council – 4 NPCs – who have all this underlying drama and rivalries amongst each other and all what different things.

Rather then play four parts I actually recruited three players from another one of my games to stop by the session that day. I gave them each a briefing on what they should say at certain points and how they should react to the other council members when they say certain things. Since they were all talented roleplayers they picked right up on it and the four of us were bickering like it was our jobs as the PC’s sat back and enjoyed the show. Finally they realized it was up to them to sort out this nonsense and started interfacing with us both as a council and as individual members. One player even took one of the council members out into the hall to take privately on what he thought was best. It was fantastic and, when all was said and done, one of the high points of the whole campaign.

one NPC may have his hands down or in his pockets as he talks, while the other scratches his cheek from time to time…

I’d rather avoid NPC-NPC interaction but some times the players just want to do that, listen in on the conversation… like the ninja spies they are…

I have done this a couple of times, so my basic rule is now “don’t even frakking think about it”. If it came up again, I’d recruit players and give them cue cards (with cues, not lines), or do what Patrick suggested.

Example: NPC1 and NPC2 are arguing. NPC1 wants to hire the PCs, NPC2 does not. When NPC1 wishes to make a point he or she asks the PCs a question where the answer supports his case, such as “How long have you been adventuring for?” NPC2 will then ask the PCs a question that strengthens his or her case, such as “You may have years of experience, but how many dragons have you slain? Our city is being attacked by an elder dragon!”

This way the NPCs are not talking to each other, but are arguing through the PCs instead. It also gives the players lots of input into the situation.

With my players, when I do the NPC on NPC interaction in front of them there is always at least one player who will interject himself/herself into the conversation regardless of whether or not they are invited into the conversation by the NPCs. My players just happen to be that way…and it usually works. Though it can sometimes get interesting if they start interjecting in the conversation of say a King or Queen and their adviser or some other personage of greater status than the PC in question.

I’ve used the different voices or props when switching between NPCs if the conversation must occur in front of the PCs. I had a few NPCs in my Shadowrun campaign with distinctive voices (I’m not voiceover actor)…and the oddest was a mage who did a children’s show where he was dressed as a clown (Binky the Clown if memory serves). I punctuated what he said with a bicycle horn. The players liked it, and it helped make my clown phobia a little better though they still creep me out. =)

Many GMs I know will seed the party with their own character, a PNPC. I think its best if this character(s) isn’t the one the party shoves up to the front when there’s a difficult negotiation. Which is why you should beware of having a smooth talking NPC hanging out with the party a lot.

I guess that’s the “high points” option.

I am also a big fan of letting the players do it. I even let them say things that aren’t part of my initial plan or notes, because it makes the job more challenging (and fun) for me that way, as I scramble to incorporate their “suggestions”.

1) Relevance. It’s easy for some people to get swept up in their own drama. So long as the GM is aware that the NPCs are there to forward the story and not showcase his or her talent/imagination/accent-mimiking abilities, then it should be okay.

2) Brevity. Watching someone have an argument with themselves can be entertaining, but only for a very short while. The GM should keep aware of how much time he or she devotes to NPC dialogue and not overdo it.

3) Audience. The best kind of GMs are those who understand their audience, can read them, and can react to them. If the GM senses the players are getting bored or not responding well to the scene, he /she can have one of the NPCs suddenly directly address a PC.

I say this because one of my very first GMs had me play three characters — basically, a human and the angel and demon on her shoulders (it was more complex than that, but the details are moot). He encouraged me to have them talk to each other, and after a while of getting used to the idea, I eventually got to the point where I would argue with myself for ten or fifteen minutes at a time (it was a one-on-one campaign; I’d never do that in a group).

It is directly because of that experience that I feel much more confident having NPCs talk to each other when I GM. It takes surprisingly little to distinguish one voice from the next; tone alone will often do it. No need for accents or silly falsetto voices.

I try hard to keep relevance, brevity and my audience in mind, though. My players seem to enjoy it when I do it (which is rare, but it does happen), so I see no harm in it.