I regularly engage in FFM and less frequently MMF.
We have a group of FWB and it took a while to establish the group and engage in the intimacies without a few problems. I live with one of the girls and we have sex together regularly as bisexuals.
You really need to know the people involved and ensure that they are happy with 'recreational' sex and not 'emotional' sex.
After some trials and tribulations Jane and I gradually found two guys and we now have another 'couple' who share with us.
Jane and I had engaged with a couple of guys at different times who were good but could not handle the fact that both of us were not interested in a regular relationship with them alone. They could not get their head around the fact we were both engaging and wanted to engage with others to satisfy our desires, even though we were happy with the times we spent with them alone as FFM or one on one.
After a few trial 'friendships' we ultimately found two guys who did not want to move in with us. Did not want exclusive rights to one or other of us, and were prepared to share the joy of sex with us as colleagues rather than as partners. All three guys are really good friends with each other as is our other girlfriend. We all share the guys as they share us without playing favourites even though Jane and I have our preferred partner there are no exclusive rights or partnerships. We all enjoy being with one or other or together as a three or foursome and occasionally all six of us together.
It is hard and there are a lot of rocky roads to travel before you eventually end up with the right people. Once you get the mix right it is an amazing and wonderful experience to share yourself with others.
We all agree it was worth the effort and troubles we endured until the 'mix'' was right for us. The group has been together for more than a year and the "couple' who share with us replaced a couple who found 'love' and decided to partner more or less exclusively. They now live interstate and one or other of the four of us have met on the odd occasion. They have shared an intimate relationship with us 'for old times sake' but it is different to how it used to be.
At first the guys would not interact with each other during a MMF. We then began to insist they engage in oral on each other. If it was good enough for the girls to swallow they needed to know what it was like. They do now but it is not high on their scale of pleasure together.