Personally, I'm trying:
Inquisitor: Lightning Knight-Enchanter
Solas: Ice/Spirit and Rift Mage
Cassandra: All tank musts and full Templar for the passives
Sera: respeced to dual-wield and items focused more towards tankiness than pure dps
Templar seriously beefs up the party with it's passives, also got the +defenses perk in Forces asap. I use Solas to get the +regen passive in the Spirit tree so rest of party doesn't have mana problems (rift mage doesn't have mana problems already).
With friendly fire on, that changes things since the dual mage party is primarily for the AoE. How does lightning work with friendly fire? None of the spells are true AoE, but does chain lightning hit friendlies?