When it has happened it has been mmm and mfm & mff. My regulars three-way at school and home are mmm so they are the foundation of this occurrence.
the mmm-s are the swimmer/diver at school, and C/QB at home. Swimmer/Diver are still together, and we still fuck on the regular. It has yet to happen, but there would be a possibility the number could go higher if the boy joined us, but the planets aligning for this have yet to happen. One of the times two threesomes happened in a day it was diver and the boy.
The other side normally has been post-party hook ups. most have been mff. the mfm-s have been me and a brother/teammate sharing a girl. I have yet to have a real mmf experience where everyone is into it and everyone in involved. Had a mfmf experience, with a brother, his girlfriend and my formal date. the four of us were sleeping a walk in closet at a vacation house. we swapped girls a few times during the night of fucking.
I wrote about the mmmf I was part of. (just three guys sharing a girl, we didn't do anything but watch the others)