Hello,
Looking at your video, it seem you swaped characters data in the kernel.bin to make this? It is a fast way but not a complete one, as you noticed. You should start working with makou reactor tool if you want to go on with your idea, it's the best field scripting tool and it also allow to swap field models among many other things.
http://forums.qhimm.com/index.php?topic=9658.0As for battle models, I would suggest you to stop swaping kernel.bin data, it turns characters into 'Nibelheim flash back Sephiroth clones', which isn't very interesting for the gameplay. I would rather suggest to 'convert' the battle models you want into Sephiroth with Kimera tool, though it can be long because most of the time you can't just swap bones and leave it as it is to get a decent enough result, and keep various animations like limits in working order.
I wrote a tutorial to begin with modeling work but it's in my native language, french.
https://ff7.fr/forum/index.php?page=post&ids=431868Unless you understand it, I could try to translate the relevant part about battle modeling bases if you would like but I don't have the time right now. Just let me know if it interest you.