I'm taking advantage of this thread to brag about the best duo position I have experienced to date: him inside of me missionary, my hands above my head, her ass on my hands and her leaning back against the headboard as he both fucked me and went down on her. It was miraculous.
The point of a threesome (or more-some) isn't necessarily that everyone is being stimulated equally at exactly the same time, it's that everyone leaves satisfied. You'd be amazed how wonderful it can be when everyone is on the same team
Edited to throw in a vote for female condoms. Q