As mentioned by Lolicon Kami there are some strategies to beating the fight. Personally this is probably one of the hardest in the game or at least it was for me since with some bad RNG on who they hit I would end up with ppl dead left and right in the first few turns.
This is pretty much a hardcore rpg game if you play it as intended especially if you wanna get the best outcome/rewards since this approach pretty much requires you to almost only live of the items you find or get in the game. There isn't enough in game money to upgrade your gear each time or at least I don't think there is since you only get back about 50% of the money you spent when you sell gear and the gear jumps a lot in price as the game progresses. But you also need ingame money at time to invest / buy stuff in the game that is not gear.
So the game pretty much forces you to kill anything you come across and get anything thats not nailed down to have a fair shot.
I mean my first playthrough had like 60-70 hours of playtime to get to chapter 5, my 2nd playthrough that I am trying right now which is a cheat run where I added +500 to all stats for everyone so I could speed through the game to chapter 5 but this time follow a walkthrough and have the "best" outcome and even with that once I got to chapter 4 and onwards I could still get killed of if I messed stuff up and the +500 in all stats didn't even feel like cheating anymore since the enemies could still hit the party for 700-3000+ dmg per hit if I don't buff the party and debuff the enemies, though even then some enemies are able to one shot some of my team members, also my playtime is still like 35 hours to get to the start of chapter 5 but now I've turned of the bonus stats and just one mistake and I have to reload pretty much.
My point here is that the game is hard, like really hard but I do like it a lot.
In case the fight is seemingly impossible for you there is a mod on the wiki that will turn all the normal health potions into an item that allows you to one shot anything, I haven't tried it out myself but it supossedly turns the game into story mode might be a nice addition to have for those fights that feel impossible. You could also like me use a save editor to add in a lot of bonus stats to your team which will make the fight much easier.
This is one of the few games I would actually recommend cheating in unless you really like the hardcore rpg style since even with a perfect run, highest lvl party and best gear + the best strategy and team setup for a fight you can stil loose over and over again which can make it get frustrating, though for some reason I usually just get angry and more competetive when this happens. Unless I've already gotten past a point before and just wanna speed through it