Loving the battle music out in the chapter 2 areas. I know for sure I want Olberic, Ophillia, and Cyrus in my PT. I haven't decided who to use as the 4th.
In your case, I would go with the following:
Olberic with Warmaster: Access to every weapon type in the game, high HP and defense. Your all-purpose tank.
Ophilia with Starseer: Best healer in the game, and starseer will provide her with a decent multi-element attack spell and some useful buffs
Cyrus with Sorcerer: The ultimate doombringer. Access to every offensive elemental spell in the game. Can use Ophilia's divine cleric skill to effectively cast six spells per turn and break enemy defenses in a jiffy (or ruin the game by doling out 200K damage per turn).
Tressa with Runelord: Can use runelord skills to transfer elemental augments to other characters. When applied to high elemental attack characters like Cyrus or Ophelia, can absolutely wreck everything in the main game with standard staff hits doing anywhere from 30-50K damage provided you equip skills to break the damage limit. She can also transfer her merchant sidestep skill to make your party effectively immune to physical damage.
I've been using H'aanit instead of Olberic because she's close enough, and Therion instead of Tressa because I selected him as my main. Therion is really, really good for the bulk of the game, but I'm trying to sub him out with Tressa for the post-game because of her sidestep ability. His steal and share SP skills are great, but in the late game you'll have more money than you know what to do with and can easily afford to buy as much as SP recovery items as you want.