So you want to be able to hit a huge fireball in the midst of a bunch of enemies, where your fighters are hacking away at them, without hitting your fighters? That doesn't really sound like an RPG to me. If any mage in any RPG shouts "I'VE GOT AN IDEA! FIREBALL!", everyone knows they had better run.
What I'm trying to say is: on the battlefield, it's a tactical choice. Get your guys out of there before you wanna do area damage stuff. In a town square: just don't hit people, don't pull the trigger and no one gets hurt.
I don't see why FF should be optional. It's not about hardcore or not. It's about rules.
Henchmen and summons: you control them.
Friendly people joining fights: you don't control them cause they didn't join your party, they joined the fight. If you want to take their lives into account, don't fireball.
