Ok, as one of the biggest sluts in Pixies, I have been the "invitee", the other woman invited to "join in", quite a lot, and I really do mean into a LOT of group encounters.
I have a lot of sex.
I had to learn what a "round heels" was, because an older woman described me as such recently. (it's a woman who's heels are so round she naturally falls onto her back with her legs spread open)
My experiences have ranged from wonderful to horrible.
I have written about some of my encounters here, but haven't really touched on the several unmitigated disasters that I have witnessed.
Guys have shown me Penthouse stories about "unexpected" group encounters that turned into wonderful, passionate "life-changing" events, and I can say they are wonderful FICTION. (mostly) The really wonderful, passionate, life changing encounters require some planning, believe me.
First;
Sweetie, if you don't know for CERTAIN that your wife is going to be open to this DON'T DO IT!
You need to discuss this with your honey before anyone else brings it up.
IF and only IF she is open to it, she will want to have a lot of say so into who she is going to fuck. If you deny her this choice it will end in disaster.
Second;
Are you thinking of simple swapping or are you having an orgy?
Yes, once she has agreed to consider it, having your friend's wife approach her is a good idea, but have you considered that while she might be interested in a group situation, i.e. two couples, with the women switching partners, with little or no pressure to be intimate with the other woman, to what Mark suggested, a total exchange of sexual power (yes, that is the word,) her reactions might be different.
Let the women set the rules.
If this offends some masculine part of you, then you are better off dropping the whole thing right now.
Third;
Alcohol is HER choice. Believe me, it is truly awful to awaken in a couple's bedroom/hotel room at 4 Am to hear unrestrained sobbing coming from the bathroom, and the words "I wouldn't have done it but I was drunk", no matter how intensely passionate she had been just a few hours earlier.
Remember that we equate "seduction" while under the influence with rape hon. Just because you (her spouse) are there doesn't change the ethics of the this.
Please understand, that I am saying this as a woman who used to meet tourists, women who where ostensibly straight, and convince them to take me to their hotel rooms to have a first time lesbian encounter. Was this sometimes lubricated with alcohol? Yes. But I made sure that they were interested bicurious, beforehand, and I NEVER, EVER took advantage of someone who was drunk. (even a slut has ethics).
To sum up;
Talk it out between the two of you first.
Then let her talk to the other woman, so they can set out ground rules.
Decide that "this is the night" while sober.
These rules are not a guarantee of no post -encounter recriminations later, but they will help.
Wanda