Turn one of your characters into a Mystic Knight and have that character cast Blizzara on his/her sword and attack. Turn another character into a Black Mage and have him/her use Blizzara. One character should be a White Mage to heal the party, and if you have Shiva, one character should be a Summoner and cast Shiva. If you want some more healing, you may want to give your Black Mage or Summoner a White Magic ability as their 2nd ability.