Bartz would have to be your masher. He'd get Dual-Wield, Rapid Fire, Sword Spell.

Faris would be the speed character. She'd get Steal/Mug, Dual-Wield, Time Magic.

Lenna Magic centered. Black Magic, White Magic, Double-Cast.

Galuf/Krile would have to be in-between, as they are both styled differently from each other. Summon, Blue Magic, and maybe Bard/Dancer abilities. Maybe have it Galuf has Blue magic & Dragoon abilities (w/ Lancet to draw the blue spells instead of the current way) & Krile could get that plus Summoner.