It is best to plan your party from the start. While planning character roles, remember "One to take it, one to deal, one to weaken, one to heal". You should have a damager, tank, entropist and healer. This will ensure you have one member taking all the damage and bringing the attention away from the rest of the party. Have an entropist (probably Merrill) to weaken and demoralize the enemy, a healer to strengthen and maintain the party, and a damager to inflict the pain. This will ensure a well rounded party that covers all aspects of combat.