deadlysnips

Try and equip all the members with asbrorb fire, water etc, and damage. Don't worry about any defensive strategies just full out attack them and try to bring them down as fast as possible. Aqua,Flara, Grounda and Winda bombs will work well or if you can upgrade to the Flarus and Groungus etc. Then as soon as you defeat them go into the characters menu and heal your members as needed. Then defeat the second one on that side and then speed over to the other two. I herd by putting them to sleep you can slow them down and attack the others.3

Your strongest attacking characters. I think I used Kiam, Seth, Sed, Jensen and Ming. They were all around level 40 I think.
If your struggling to beat them try getting to Uhra with Tolten and going into Gongora's secret cave and use that as a leveling up ground.