OP: If I understood your question right it was more of "How do we get started?" A lot of couples seem to like that to be girl/girl play then the guys join in, but that doesn't work you (or us).
Something we have gotten asked is, "So, do you just go into a room and get naked and start playing". Though it sounds kind of weird, generally that does happen. Certainly some light touching and/or kissing (if you allow that) will help set the tone and mood so that it doesn't feel awkward or mechanical.
We have been with couples where we started with same partner and someone simply asked, "Wanna switch?", and we did. We knew going in though that we'd both be fine with that so neither of us felt like we were being put on the spot. It's something you want to discuss and know before going in, but keep in mind the atmosphere and action can alter the way you think if you're kind of on the fence.
Generally, starting with your own partner will feel comfortable and natural and once things are underway, it will feel less awkward to swap in the event everyone is up for it. Once you have been with a couple it gets much easier, assuming everyone enjoyed themselves the first time.

