It's really not that hard. But if you've been using as much people as you can I suggest you move everyone left and up and take everyone out there while having Ike guard the western fountain entrance. Then once they're all taken out, go counter-clockwise to the right and kill those guys while you move Ike to the Southern fountain entrance. Once they're all dead, charge north and draw Bryce to your strongest unit, or Ike if you can heal him. After you've killed him, order everyone into the bottom right square for safety except for your physic users. Keep your physic users 25 spaces away from Ashnard and have Ike draw him in while healing Ike every attack. Now its just a game of leading Ashnard to the top of the stairs or, wherever you want that's safe for everyone.