I don’t know this area but have you considered a bothy?
No problems having a fire,
They have ready made fire places
And if the weather turns for the worse you can sit comfortably having a beer and a few tunes on the guitar
Whatever you decide to do post us up a few pics or a trip report, be nice to see how you went on
I can't help with the camping, but the bothy idea is not a bad one, RaferJefferson, as there are only 6 of you. None suitable in the Brecon Beacons area, but a quick look on the
Mountain Bothies Association website reveals that there are a few in mid Wales.
One listing stats "Camping and fishing by permission of the estate only- Estate Office 01597 810449" - a possible opening for wild camping?
https://www.mountainbothies.org.uk/bothies/wales/lluest-cwmbach/PS - a shame that you have had a hostile reception, as you do state in your post that there are only 6 of you. I have to confess that my initial gut reaction was hostile; I've seen the aftermath of drunken camping parties down at my local beach here in Orkney, and stag parties do get a bad reputation.
Good luck, and all the best!