Your levels are perfectly fine. However, if you didn't get all the nice abilities from skills, you may be in trouble.

Jessica doesn't need Kazing, it just helps. I believe she gets it from Staffs, as I always powered up Staffs for both of the Mages.

Hero learns Omniheal from...Courage? I don't remember, but it's a very useful spell, I believe you get it from maxing out Courage. If you don't have it, that's fine.

As for Miracle Slash, you get that from powering up Swords. Since I always just powered up Swords and Courage for the Hero, I got it rather early. If you don't have it, use Falcon Slash or just a normal attack.

One Sage's Stone is just fine, but two isn't really neccesary. If you do have one, you don't really need to worry.

Most of the things I mentioned are pretty optional, but here's what I always do:

1st turn: Hero use Sword technique, Yangus use Helm Splitter, Jessica use Oomph on one of the fighters, Angelo heal.

2nd turn: Hero use technique, Yangus use Helm Splitter, Jessica Oomph the other fighter, Angelo heal

3rd turn: Hero use technique, Yangus use Helm Splitter, Jessica use Magic Barrier or Insulate, Angelo heal.

4th turn: Hero use technique, Yangus use Helm Splitter (this is what you do until defence is only decreased by 1, then just use Parralax or some other technique), Jessica use the other buffer or just use a Sage's Stone, Angelo heal.

Repeat, and revive when necessary. Remember to reapply Oomph when Rhapthorn uses the 'wall of ice' or it just wears off.