I have done plenty of parties, so the thought of a MFMF session doesn't concern me. And no, I'm not bi in any way.
In many ways, I see this as a better possibility than a MFF session for me, for the reasons I posted on the 'threesomes - every man's dream' thread - https://www.ukpunting.com/index.php?topic=51488.msg672871#msg672871
The advantages to me are that you can get off on 2 hot girls for half the cost (with the other male contributing). All the better if the girls are genuinely bi and there is a possibility for daisy chains etc.
I guess the difficulty is finding 2 girls willing (who may have experience with each other), a suitable venue and of course a suitable fellow male punter.
I'm no expert, but I'll give my two pennorth. These are tips from my own experience, not rules. There are no guarantees that you'll have a great session, but if you can keep to most of the tips below it should greatly increase the chances of a good MMFF punt.
My first punting experience was a party, it took ages before I did a solo booking (it was shit, but glad it didn't put me off). If you're unsure of how you might feel fucking a girl in the presence of another bloke or seeing another MF couple fucking in front of you, try a party first. They're good fun and value by comparison.
Arranging your own thing guarantees the ratio and the services to be provided. Parties, unless you're lucky will not have the same low ratio and almost certainly not the same services. Bespoke bookings are much more full on by comparison.
They can be a pain to arrange, not always, but they usually aren't a last minute thing and require a fair bit of prior planning. You can strike lucky though. I've had more than my fair number of failed at the last minute group bookings through no fault of any of the parties. Shit happens so to speak.
It helps massively if the girls have met before (ideally several times) and you know that they get on and work well together and are keen on these type of group bookings.
Same for you and the other punter. Don't go booking two girls neither of you have met before. You might strike lucky, but that's highly unlikely. The greater the rapport everyone has the better. Trust matters in these sort of meets.
Longer is better generally, 90 mins at a min, and probably best if everyone has met before. An hour IMO would only be doable if everyone knows everyone else well.
Communicate, establish ground rules. Decide for yourself what you're prepared to do, and what you might want to try e.g. for some, two MF couples fucking in the same room (with swapping of course) might be enough. How do you feel about spit-roasting the same girl with another guy? Fucking one girl cowgirl while the other guy is stood getting OWO from her above you? Both of you DP'ing one girl?, etc., etc.
Most importantly, relax, get comfortable, get in to the moment. There's no need to get stressed or feel intimidated. Enjoy the session for what it is.