Uhm because I am playing ff6 for the first time I think I have some suggestions
You could do without Cid, I think he is not a very important character in this final fantasy, sure he has some minor scenes but that's about it.
I think Ultros (the purple octupus) might be a good one to add, you meet him on various occasions and have to fight him three or four times. Also the things he says and his evil plans are just hilarious.
Oh and Maduin, Terra's father, you get to play with him for a little while in the esper world.
As for ff2, maybe Borghun might make a nice addition.
Lastly, since the ff1 list is kind of short, you could add Bikke the pirate captian, or the four fiends, Lich, Marilith, Kraken and Tiamat.