Try telling your Seraphim to Engage at Range and Focus on Attacking. They'll only stop casting offensive magic if the fight moves in their direction, either to run away or to do a bit of melee and then run away. Also turn off Lailah's close range spells and Edna's trigger spells if you're doing this. Lailah would run into the boss's attack range before starting to cast those, and Edna wastes time by setting her triggers over and over and over again without actually attacking.
Human AI should just aim at weaknesses. Like...all the time. There's never a reason for them not to be, especially since they can hit everything. Unless you want them to cast spells while Armatized. Then use Engage at Range like with the Seraphim. I always have Human AI's attack frequency on Balanced, since I don't want them right in the enemy's face at all times. They die even more often when doing that.
Tell everybody to Watch HP and use Blast Gauge for defense. Seraphim will heal and Humans will use Armatization when HP falls below 75%. They'll un-fuse when it's higher. There also seems to be a slightly lower threshold for Armatized heals. Like, if they're sitting right at about 75%, they won't heal themselves, but they won't unfuse either. They'll heal themselves if they get hurt too much more though.
Seems nothing can be done about the fact that all party AI can't dodge enemy attacks for crap in this game.
In normal battles I have Edna and Dezel fighting on Close Combat while Mikleo and Lailah balance their melee and spells. (And I have all of Lailah's and Edna's spells turned on since they work just fine in this situation.) All four of them with balanced attack frequency like the humans. The humans set to Manage HP instead, so they Armatiize at 50% health instead of 75%. Other than that, same settings as with boss battles.
