Instructions
Attack the three swordsmen first. They are at level 11 and level 12, and have only 615 HP a piece. Defeating them allows you to concentrate on Judge Ghis without incurring extra damage.
Use a gambit or a spell to make sure each team member has Shell and Protect cast on themselves. These spells will reduce the damage Judge Ghis' attacks cause. Recast the spells as necessary whenever they wear off.
Cast Disable whenever Judge Ghis erects his protective barrier. If you cast Slow and Blind, you can reduce the likelihood of Judge Ghis casting his barrier spell. Recast Slow and Blind quickly whenever they wear off.
Attack Judge Ghis with physical attacks. Judge Ghis has no magic spell weaknesses, so focus on physical attacks. A barrage of physical attacks will eventually weaken him enough to end the battle.