This battle begins with 4 your the 8 allies (Jude, Milla, Rowen, and Leia) and everytime one is defeat another will take their place. The hardest part of this fight is the ease of getting surrounded and defeated without putting up much of a fight. Attacking recklessly will only lead to another person sneaking up behind you and getting in a chain of attacks, so you'll want to make sure you attack wisely.
The easiest way to defeat your allies without getting surrounded is to juggle them in the air, where you are immune to the attacks below. Start by using Crimson Fury to launch your allies and then then use the sledgehammer's Swallow Flight to launch them higher. Make sure to switch weapons and artes to keep them weakened and in the air and when the chain dies back off to recover TP, either by using an item or getting in taps on the enemies when safe.
Don't forget your Chromatus either, which you can use at any point to save yourself from a combo and then focus on aoe attacks like Hexentia and Apocalypse.