I've been having a lot of trouble with the three Flaming Fist dudes just a bit south of Beregost. Died many times, even using strong stuff like wand of lightning from Neera and Bless from Jaheira. I looked it up on Google, and the results indicate that the leader of this group is supposed to accost me with demanding questions rather than attack. However, as soon as he's on screen he gets a red circle and they attack us even if I keep making the group move so as not to not attack. I thought maybe it was my reputation, but it's 13 for all 5 characters in my group, which the game says is "popular". Hoping for a solution, I can't kill them. Neera can get one blast of the wand off to kill one but the other two slaughter us before she can take out another. Jaheira is level 2, everyone else is level 1.

I'll second the use of Sleep. It may be able to down all 3 of them. Sleep can transform a lot of these early encounters from 'Hard battle, probably lose someone' to 'eh, just slit their throats, grab their gear, and lets move on'. Color Spray looks similar, except it has a different AOE and it might not be party friendly.

You could also try using Entangle from Jaheira and Grease from Neera; both spells may slow them down long enough for your party to cut them down with missile weapons.

What class is your character and who else do you have along?

Edit: Why can't you kill them? Is it a "I refuse to kill them", or a "I literally am unable to kill them [before they kill me]?"

You can simply walk around or run past them and return when you've become more powerful.

It looks like OP can't do it. He shouldn't kill them even if he could. Being a cop killer will bring your rep down to 1. At this point everyone will attack him.

I was assuming it was more a lack of ability than a lack of motive, but I figured it was worth asking. If the problem is 'ability', then Sleep will let you kill them with near impunity; just set everyone on each sleeping merc in turn until the kill is made, then move to the next sleeper.

Judging from this (check the comments), these particular Flaming Fist mercs don't cost you rep. Most of Flaming Fist kills will cost you serious amounts of rep (rep which you can buy back at a temple, if need be), but there are a few that you can kill with impunity.

It's also really bizarre that these Flaming Fist just start off hostile. Do you have an older save that you can revert to? The only possible reasons I can think of for them starting out hostile is if your reputation is too low, OR you somehow managed to ping one of them with an AoE spell off the screen before you even saw them, making them hostile. (A third possibility is that you somehow Charmed one of them in an earlier encounter, the Charm spell wore off, and as a result they are now hostile to you.)

Mercenaries out in the "countryside" don't cost rep. if you agro them, only town/city members proper.. I've never come across this in the original. May be an EE thing.

I recently started an EE playthrough, and the guard OP is talking about questioned me and let me though without any trouble.

It's been years since I played the original BG, but I'm quite certain he was there too. It's a Flaming Fist mercenary who accuses you of being the bandits troubling the Sword Coast. You can avoid combat with the correct dialogue options, but if he turns hostile 2 or 3 more Flaming Fist spawn and attack you.

I'm pretty sure Hickory is referring to the guard starting off hostile (therefore not talking first), not that the guard exists in that area.

Yes, of course he exists. He is part of the game. The title of this thread is, "Flaming Fist south of Beregost attack automatically". Note the words 'attack automatically'.

Aha, I just misinterpreted what you wrote. I read it as "I've never run across that guard" rather than "I've never encountered the guard starting off hostile." All good, carry on!

Not true. It depends on the coding. I think this encounter doesn't cost you, but if you harass the one at the mines (where you have to bring a body to the FAI) would.

The problem can be caused by either a bug, or previously giving the wrong reply and running away.

Either restricting movement (sleep, entangle, hold, charm) could be used, or just the plain old "chase this character while I plummet you with arrows" strategy.

Explain where you mean. There is no body at the mines. The only body you have to return to the FAI is Samuel the deserter at Gibberling Mountains. Those mercenaries do not cause rep loss.