Tzardok I may have better quality equipment than the average player, and I'm not always the best at working out tactics... Perhaps someone else can work out a better plan.
I'd strongly consider equipping Simon with the Eldritch Ribbon, assuming you have it. Then I'd look at equipment loadouts that increase MAG for Carina. Using Vhala and her gang debuffs may be a good idea if you are having trouble keeping the party standing, and her Anti-Sex aura can double as a healing spell. Another possible loadout is Simon, Qum, Robin, Carina with Qum buffing and using Pretty Lance on sex vulnerable enemies and Robin handling elemental damage. This at least gives you more options to keep the party standing.