To add to Aidoru's description:
Blue Expert (overdrive gauage with 1 orb)
Normal Overdrive: Damage to entire party + Rot debuff
Raging Overdrive: Damage to entire party + Undead debuff (heals damage affected targets, 3 turn duration)
Red Expert (overdrive gauge with 2 orbs)
Normal Overdrive: ~2400 damage to 3 targets
Raging Overdrive: Damage to entire party + Instant death debuff (death after following turn if not cleansed, Regen can recover the target from 0 HP)
For Blue Expert, the overdrive gauge is 1 orb, so it can overdrive every 2 turns normally, and every turn while Raging. Black Propaganda should be viewed as mandatory for both Experts. In addition, Sol's heal is ineffective against the Undead debuff, since the heal applies before the cleanse. I recommend Behemoth eidolon for both fights, and 2 sources of cleanse for Red Expert.