You could make allies, but it would take an incredible long and complicate script for each character. Basically, you'd have to set hundreds of variable, find a way for the ally to locate an enemy, set their "try to reach" mode to track that enemy, change the animation, use about 2 dozen variables to determine damage, hits, etc. I thought it through and I think you could make it work...but would you want to? I don't.
I am doing a game with multiple characters, but you only play as and control one at a time. I may have the other characters follow when they would be present. All their stats are stored in the variables. I'm also routing the current leveling system for one of my own design, because I wan't the stats to reach high numbers (ala Final Fantasy in numbers) and have more control over leveling, if anyone has suggestions on this I'd appreciate it.
My current side project is a system in which you jump to a new screen when encountering an enemy. Then the battles are turn based, with a party. Its possible, but I have to completely ditch the current battle system and create a new one with reams of "code" (we need a good word for what you do in coldstone, cause its not really coding or programing), I'm just plugging it into the defaul game for right now to test it. I know how to do a lot of the stats stuff, but I need some help with random monsters and stuff. Any ideas?
Oh, and if you plan to use an item, have it cast a spell. There's more stuff you can do with a spell.