My wife and I have done this in the past and it turns her on immensely to do exactly what you said and to see me actually have sex with the other woman. You may or may not get jealous, but you both need to be mature, constantly talk and have a safe word to get control of any situation you are in. A few things we did.
One, we started really exploring this fantasy by watching FFM porn together and talking about how hot it would be to do the things were were watching. Talking and seeing and feeling the reactions of each other was extremely hot.
Two, when we did move forward with this my wife was in control. She was in charge, she led the action, she suggested things. This way each thing brought to the table was something she felt comfortable with at that moment.
Three, I understand finding a unicorn can be extremely hard. And, we did not want to include any friend or any other person that could be some kind of connection. So, we hired a pro while on vacation in various places around the US. No connection, we knew exactly what we were getting and the pro left right after everything was done.