Pony Fantasy VI Remake

if the sprites don't display properly in US, how can I give them properly sized molds once I begin replacing those images? Do I just need to keep track of how big each individual image is?

FF3usME is not open-source. There is no way really to fix this, unless you use something like IDA Pro and change the code at the assembly level. Keeping track of the size of the monsters is the almost the only thing you can do.