Separate your groups again. Assign DPS to a group. All the players should go to defend. An announce will be made to tell wich sorceress is preparing the attack which gives information on where the attack will be made. Once the attack is under control (still killing mobs) an announcement will be made telling that the sorceress is weak and open to attacks. Second group should run to her and finish her ASAP or that attack will be repeated. Once group one finishes players should join gorup two to finish sorceress. This will repeat each time for a number of times until the battle is won

Split your group in two. All 6 players should go for the attacks. When a second attack is called one of the group goes to take it while the first one finishes the fight. Then first group goes to aid the second group.

Just kill fast