Ive been in MMF 3somes (civilian) but never in a '1 in the pink 1 in the stink' DP, or both in one at the same time. Never had much luck with ladies into Greek period ... poor me. Done the 'fingercuffs' thing (one oral and one vaginal from behind) and once where the lady got us both in her mouth .. didnt bother me.
As an earlier poster stated, it takes a lot of trust by all involved, and as another poster stated, the lady has to be in the mood. Once you kind of figure out the logistics and mechanics of it all, things can get hot quick! In my experience, some inadvertent momentary male/male contact is inevitable, but no, it hasn't made me "go gay" yet. I love doing because if a gal likes to do it (and isn't just experimenting), she REALLY loves it and it makes for a heated session.
Hmmm back in the GOOD OLE DAYS, a friend of mine took me to a bar. Lots of nice ladies there. He apparently knew some of them and invited a nice skinny one to have a drink with us. Well next thing were in a room and taking turns who get back end and who gets front end. I thoroughly enjoyed it. She did to with all the moaning on my dick!!! (BOTH ENDS)
I was offered a MMF one time with an ex-girlfriend. He had no idea, so I had to decline. Otherwise, apart from what I posted earlier it has been toys and me (both anally and vaginally)!