I just beat the quest and i know what you mean about a heart attack. After i saw it was ivory lagi by itself i figured it would be one at a time. WRONG. Although i forgot to cook out my -55 thunder res so ivory lagi was actually harder than the second part. I unfortunately spread the damage between azure and brach too well cause azure died 3 hits after i finished brach. I had 1 death and most of my healing left and it took me 35:11 to beat it. That fight physically exhausted me. You have my respect if you beat that with only high rank gear.
I started the quest without much knowledge of the fight, I had read they were G rank level, but forgot about it. Once Ivory Lagi hit me and took 40% of my health out I knew something was wrong, so I checked and they were G rank for sure, that's when I got a bit freaked out. >_>
It pretty much took all of my potions to kill Ivory Lagi, then I scrambled for extra pots from him and the gathering points and when I saw Brachy AND Azure Los come in at the same time, I knew I was in trouble. The whole fight I took a few pot shots on each one when they were tired, but for the most part, I just ran around in circles while they tore each other apart. Brachy was actually the one who killed Los, and after he was dead I literally had no pots left and was a hit away from dying.
Once Brachy got tired, I ran up and put a Shock Trap down, popped a Dash Juice and did a single Demon's Dance and he was dead. Apparently Los did a number on him too, and I suspect his own slime puddles did a good bit of damage to him.