Have done this numerous times when I used to frequent the old surfboard factory (Burswood swingers) and Deltas.
Normally the standard one guy in each hole, however the best I ever had was when I was in invited back to a couples place in Belmont with another single guy and a two other couples. It was a night of full on sex. Multiples on the bed, girl on girl, and my first time with the double in the pussy, before prolonged swing fun taking it in turns with the husband and another guy pounding his wife in a swing in their back patio in the early hours of the morning. At that stage there was no way I was going to cum (had already cum several times) and normally I wouldn’t be able to keep it up, but the sexual tension was huge, so I was rock hard. We did this for over an hour and she was screaming and having multiple orgasms. I wonder what her neighbours thought!!
To note, I’m very straight and have no bi tendencies at all. And yes there was some close contact with the other guy, but I was so focused on her that it didn’t bother me. Posdibly the best sex night of my life!