Well, I already tried a few different changes in equipment, with one more focused on MAG like the guide said and one a bit more defensively focused, which changed... not a lot. The equipment at the last save is:
Simon:
Durge Sword
Ancient Glove
Dwarven Helm
Lustplate
Heirloom Pin II
Altina:
Staff of Stone
Enchanted Wand
Crown of Lust
Lingerie de Iris (the status effect version)
Sexual Charm II
Carina:
Crusader Staff
Shinning Sphere
Green Hat
Erosian Priest Robe
Amulet of Alchemy II
Riala:
Elegant Whip
Buttplug
Property Collar
Revealing Negligee
Greater Magical Necklace
Stats without equipment and before the first fight:
Simon Lv 91, HP 6,868, MP 786, ATK 228, DEF 176, MAG 141, MDF 196, AGI 328, LUK 207
Altina Lv 89, HP 4,226, MP 1238, ATK 103, DEF 103, MAG 179, MDF 143, AGI 293, LUK 289
Carina Lv 89, HP 6,217, MP 1,388, ATK 111, DEF 148, MAG 176, MDF 181, AGI 189, LUK 349
Riala Lv 89, HP 4,661, MP 1,509, ATK 110, DEF 105, MAG 183, MDF 118, AGI 324, LUK 192
All of them level up once after the first two fights. Does this help?