My question is how assertive is your wife, and how assertive is the wife of the other couples? I find my most successful experiences is where the other female is as assertive as myself. It seems like this would be even more imperative if g/g is more of the main focus. How much of a participant in the conversations is your wife? If she finds them attractive does she start flirting at all? Is the other female flirting? When your done with your initial meeting how do the goodbyes play out? Do you just shake hands? Give each other hugs? I really like it when the other couple give hugs, it tells me a lot. Hugs tell me they aren't afraid of physical contact. If they seem uncomfortable with a hug then how on earth are they going to be comfortable naked and giving pleasure. Pay close attention to body language, not just their's, but also yours. Don't forget to flirt with each other too, they want to know you're into each other. Make sure you always seem open and inviting.
I think conversation topics are important too. It's good to find common ground but once that's established talk about sex, that's why you're there! The more comfortable everyone is about talking about it the more of a chance everyone will be more comfortable with doing it. I always ask how they got into the lifestyle, what started it all. Talk about what excites you about it.
The most important thing is BE POSITIVE!!! Positive people are more sexy than negative ones anyday. You'll find your niche, you just need to keep your chin up!
Good Luck!