Friends watch each other

I've always had a fantasy of having sex in a room with another couple but not actually sharing partners. I'm not exactly sure how it would play out but something like this. We are a mixed race married male-female couple ( her darker skinned, me pale white ) and she is pretty shy and and reserved publicly. In the fantasy we come back from a fun night out with another couple around our age we know very well and trust ( say late 30-early 40 ) and they are different physically to us both. We've all had a fun night and a good bit to drink. Talk is playful and there is lots of touching. We go off to fetch more food and drink and when we return the other couple are making out pretty heavily. This turns my wife on and we stand in the shadows watching them. Things start to get heavy with both couples when the other couple spots us. They ask us not to be shy and come watch them. My wife is very unsure but I encourage her to go along and that nothing will happen she doesn't want. They perform sexually for us and there is lots of eye contact, talking between the women about how different they are, how it feels, how different the men are until my wife is so turned on she starts to relax and allow us to perform for them too. Talking is a big part of the fantasy. The other couple are more exhibitionist and do things we haven't like anal etc. The more adventurous woman teaches my wife new things. We only watch and talk, and we stay with our respective partners throughout.