I checked out the JP wiki entry for each Ragnarok, and I'll be going with my typical core team for each. Chaos Magic as EX and Jorm as friend eidolon for Rahab, and Maiden's Prayer and Behemoth for Medusa.
Team: Mordred, Triton, Gabriel, Shiva, Sol

The strategy for Rahab is to keep the attack buff off and delay pushing into Rage until Burst is ready. For Medusa, you want to push into Rage ASAP because the poison debuff from the normal overdrive is deadly when comboed with petrification. After that, it's just a game of chance. The Amon cheese doesn't work in Ragnarok since you only get one usage and the boss is much more durable, so bringing her along is not as useful unless you're Fire. Rather than trying to prevent Petrification, focus on damage output. The sooner you get her to Stun, the sooner the Petrify barrage will stop. Don't expect to win every time, as there's no defense against 4 Petrifies in a row.