I don't think Rydia has learned Meteo yet anyhow...from what I remember it's not until somewhere in the 60s...maybe 66 I think I remember once. I am guessing your HP levels are around the high 3000ss for Cecil and Kain.
So far the advice here has been good. It shouldn't be too hard to do. Have Rydia use Nuke. She always seems to cast this spell VERY quickly when I play. Rosa should heal and use White/Holy. Edge should dart everything...including the Masamune since he won't need it if he's darting.

The only other thing I would tell you is to gain more levels. Get you HP levels for Cecil and Kain around 5000 and it should be easy