What Eliont said, though you're suppose to follow the tip. For the first one, you need to target the back row cuz they're the ones dealing the damage, while the front is tanking. Basically, you'll probably want to equip Abbie (The 3* Earth piglet) with the pre-reg gear, and use Naam for the middle (cuz they're both water).
I had almost beaten it (only need an attack or two more), but too much of my gals were taken out at the beginning, so they beat me in the end. Beat it! Now, wonder if I should save that evolve stone, or use it on Snow....