It's really hard to make this game in RM2k3 because you need battle sprites and there's very few of them out there compared to other resources. I bet you can find Cloud and maybe one or two other characters, but you won't find all 9. You'll have to make them yourself if you want them in battle. Otherwise, google is your friend. Just search for "rm2k3 resources Final fantasy" or something among those lines. You'll find lots of sites.

That goes for both of ya.

edit: Aeris, Cloud and Sephiroth can be found here