There's always the old classic:
Aikido in everyday life
Terry Dobson, Victor Miller.
Berkeley : North Atlantic Books, 1978. - 356 p.: ill.
Other than that, I haven't delved deeply into that particular discipline
. Just studying aikido, and other disciplines like zen, taoism, and going to the pub and dealing with people in general should teach you all you need to know and do in such a situation, IMO.
When tempers get heated all around, it's not so much what you say, but how you say it. I mean, when you're going "look, let's all just stay calm and solve this like civilized beings" while at the same time your eyes are darting around looking for the nearest exit, or you're saying it in a very harsh, commanding tone of voice, the effect will be quite the opposite of what you intended... there's no magic formula.
Just stay calm, stay centered, be friendly, open and honestly caring, and clearly show that you want to help work this out in the best possible way - and of course, be ready to pin down the first idiot who doesn't quite get the message