FF6 with FF5 job system, NEED HELP

I don't see why having so many sprites would be impossible, or even hard really.
That being said, I still think it would be worth it to have the same class system with working sprites for each character and class.

In the shortest way possible: No.
Longer version: The game doesn't have room for that many sprites. If you were willing to completely rebuild the entire graphics engine from the ground up and then reassemble the various pointers from the core battle and event engines, then I would upgrade my response to "Probably No."

I understand you're excited about hacking and FF6 is a surprisingly flexible game engine that can do a lot of things (but is also hampered by some hilarious shortcut coding). However, there's a few things that are more trouble than they're worth due to the limitations of the SNES ROM format. Top of that list is "Adding something new without replacing something". So you generally won't ever see any hack that adds new characters/graphics/items/spells/espers without deleting a few things that were in the original. Some very high level coders may eventually get around to adding a new PC or two since that's something which is in very high demand, but on the whole, it's not likely worth the effort it would take to adjust the ROM to allow for more characters/items/spells/espers.

Adding enough graphics to give every one of the 14 PCs in FF6 more than one sprite is likely to be the last thing that ever happens short of turning the whole game into a first-person shooter with Mode 8 graphics~

Now, building a Job system in FF6 is sorta-kinda possible thanks to Gogo's skillset swapping... But changing graphics for every job? If you can give up on that part, you might be able to make something if you're really dedicated.