My girlfriend's roommate used to join us. They'd been doing each other before I came along, sort of a friendly roommate thing, so it was fun and easy for me (two women NOT helping each other out is work). Once in a while they'd take turns with the toy up the rear. For my part, I loved the vibration coming through wall. And they both came harder which is what I get off on the most.
That two-man thing looks weird and awkward.