NOTE (in case this doesn't get edited): read "Prince" and "Hero" as Nick and Deanna respectively (this is in case you named them differently).
Here's the first part of the way I dealt with the museum battle in which you toast (not in the cordial way mind you) Bazoo, Death Waldol, Solo, Barbara, Danton and Gordon. None of my characters was built up very high except Sarah who got built way up as I perfected the total battle technique and she cast a lot of auras with the concommitent experience gain. I gave Claude the running ring while the protect and white rings went to our fearless leaders (prince/hero).
Move 1 - Prince - up 8, left 1 and cast bolt 4 on death waldol
Hero - up 8 and cast bolt 4 on death waldol
Wendy - up 5 and cast freeze 3 on death waldol
Natasha - up 5 and cast blaze 4 on death waldol
Sarah - Loiter witlessly for now
Shade - 5 up and attack solo
Claude - 6 up, 2 right and attack solo
Ruce - 5 left, 1 up
Dawn - 7 left
Jaha - 6 left
Luke - 5 left
Eric - 4 left,1 up, 2 right
After this turn, Solo and Death Waldol should be history. Bazoo will be trapped so he can't join his co-conspirators in crime Chu Rao and Evil monster. Gordon the pathetic will be marching to his doom while Barbara and Danton will be facing the lesser hosts of your avenging party.
To finish these cretins up, do the following:
Prince and Hero can whack Bazoo while Wendy and Natasha can first cast attack (keeping out of range of Bazoo's magic though) on them and later move in close to help dust Bazoo. Shade can backtrack and attack Barbara while Claude can take out Gordon. Sarah should cast aura 4 as needed and the rest of the gang can work over Danton and Barbara. If you find that some of your characters bite the dust, they probably just need their levels boosted a little. (Natasha and Wendy may need to be levelled up to get their respective attack, blaze and freeze spells to the proper levels.)
After defeating the first sextet of scalawags, you will now be ready to take on Chu Rao and Evil Monster. They are a lot easier without Bazoo to complicate matters. Heal up anybody that needs it and keep everybody back at first. Cast attack on Hero and Prince and send onc of them in a little closer to Chu Rao (but out of EM's magic range). If the other one can move before Chu Rao, place them in a diagonal postion to each other. Chu Rao will come out and generally use a physical attack. Bash him with Prince and Hero and send in Wendy, Natasha, and SHade with ranged attacks to send Chu Rao to whatever heaven he believes in. Then heal up and wait for the attack spells fo wear off. Cast attack on Prince and Hero again and bracket EM on both sides and flail away. EM will only attack (at least I've never seem him use magic here) with physical attacks which do only little damage. Once EM is weakened, you can send some of the otheres in to help if you like. After EM is gone, heal up and wait for the attack spells to end.
Keep everyone except Prince and Hero below EM's yellow square for now since Kisiringi's magic has a long reach. Cast attack on both Hero and Prince. Move Prince up the square that is diagonally down to the right from the yellow square where scorpion Waldol started. Move Hero to the square two down and one to the right from Prince. (Move Prince into position first since this will affect how Kisiringi and Frabell move). Kisiringi will move next to Prince and do mostly physical attacks while Frabell will move below her and attack Hero. Move either Natasha or Wendy to the left of Prince (keep her well away from either Prince or Hero so as not to offer Kisiringi a target for her magic) to cast attack on Prince again as needed. THe other one can support Hero in a similar fashion. Fight Kisiringi and Frabell and send in Wendy and Natash with Feeze or Blaze when Kisiringi is weak. She is your primary target since Frabell's magic is not a threat like Kisiringi's is. After Kisiringi falls, Frabell will soon follow suit.
Now you are set to tackle the three Faces of Eve (er Iom). Send Shade in to attack the little Ioms from a distance. You can cast attack on him to speed this up. While Shade is attending to this chore, heal up Prince and Hero and let your magic casters recharge a little. Once the little Ioms are gone, recall Shade and cast attack on either Prince or Hero. THen send him in to attack big Iom. Have him attack once or twice (depending on how Iom attacks and how much damage you suffer the first time). Move him out, cast attack on the other one and send him in. Heal the first one and repeat this cycle until you are done with Iom. I don't send in any one else to help since Iom's attacks are so strong.
You next mission is to take on the triad of Waldol, Warderer and Bulldor. This is probably the hardest group to take on in this stage. To do this, you need to first drain off Warderer's magic so he can't attack you or heal Waldol. Then you need to cut out Waldol from the pack and do him in by himself. Move Sarah, Luke, Wendy and Natasha to the area well to the left of the square where Warderer started. Move Prince and Hero to the area below where Warderer started. (Keep them apart so Warderer's bolt spell can't hit them both at once). Then move one of them to the square that is two squares down diagonally to the right from Warderer's starting square. Warderer will then move and cast bolt twice on your guy. Move your now injured guy back to luke and Sarah for healing and move the uninjured one in. Warderer will return and cast his last magic attack. Move back to Sarah and Luke for healing and you are ready to take on Waldol. Move Prince one square to the left of the one where you lured Warderer out and have Natasha or Wendy move back from him and cast attack. Then move Hero to the square above the yellow one where Warderer started. Waldol will then come and cast demon breath twice. Then send Prince up to the left of Waldol (not below or Warderer will join in the fray) and attack. Send Hero back to Luke and Sarah for some well deserved r&r (whichever one he likes or both - who knows how his tastes really run?). Prince should continue to attack by himself (sending any one else in will only encourage Waldol to use demon breath). Waldol usually will only use physical attacks on Prince. Be prepared to retreat Prince, heal and repeat the process or use Aura 4 if Waldol does use demon breath. Once Waldol has gone to meet his maker, heal up Prince. Then cast attack on Prince and Hero and, backed by Wendy, Natasha and Shade, send them in to send Warderer and Bulldor to the happy hunting grounds.
Now all you have left is Geppel and Dava. Heal up, cast attack on Prince and Hero and use them lure Geppel off his position to one beyond the range of Dava's magic. He will quickly fall to Prince, Hero, Natasha, Shade and Wendy.
Take a deep breath, heal up and recharge Wendy and Natasha if needed. Sarah shouldn't need to recharge much if you still have the healing rain (I always give it to her to carry) from earier in the battle. If not, take your time to let her build up a little. There are two ways that I've used to put an end to Dava's miserable existence.
A) Use Prince and Hero to attack her the same way you did big Iom until she begins to cast Dava aura. Then send everyone else in and she will be history.
B) Have Wendy cast attack on Prince, Hero, Shade, Claude and Jaha and perform a mass attack on Dava from all sides. If she manages to survive the initial wave, send in Natasha and Wendy to perform the coup de grace.
In either case, have Sarah cast Aura 4 or use the healing rain as needed to keep your whole party alive for the joyous victory parade through downtown Granseal.
Hope this helps someone since it took me a while to come up with this strategy.