If you decide to go through with it drinking a bit (or otherwise un-sobering yourself) may help you have a 'moral excuse' for yourself if you ever regret it down the line ... "well yea i did, but i was really drunk..ect"
Haha- If ya wanna talk about the ups and downs of getting involved with a married couple, shoot me a PM. I've been in a few 3somes with married folks and I might be able to answer some questions you might have. But for now, I'm too tired to think. I'll get back to ya later.
I would wait a week. If it still makes sense then maybe do it. For the record, I find that I'm in a clearer mind *after* the orgasm than before.. Maybe you'll want to induce one before making any big decisions.. Hell..Induce one anyway...
It could be fun. If you're comfortable around them, go for it; if not, tell them you wouldn't be comfortable with it. You should definitely return the call, it may not be what you think it is. (Just keeping it optomisitic for you.)