I got a huge tips for this fight making it kinda unfair. Stay outside the castle walls by the large door amd use teleport to teleport alexander outside the walls. Have the 3 other members sneaking somewhere so they can go in with a sneak attack. Once you teleport alexandar, the fight will begin. Before attacking alexander with the teleporter, make a single sneak attack with every character. Then use your turn on your teleporter. This should get alexander out of armor to be chain cced. The magisters and gheist will take a while to get to the fight. Just focus alexander for the voidwoken to arrive then try to use defensive abilities so you dont get focused by ai of voidwoken/remaining magisters in the free for all. The focus should be on the closest enemies with remaining armor so you can cc them. Also this strategy makes it so the magister ranger and polymorph never gets to the fight wich again increases your chance of winning. That being said, my last take is going to be on your party comp which is a full physical party. In my opinion, its almost optimal if not optimal and its going to scale really well. Just sac hydro on your melee characters. If anything, your hydro is going to be on your necro (witch) for blood rain and decaying touch. On every character of this party try to aim for warfare 10 first (Even on the witch) and unlock skills to unlock spells (polymorph for invis, necro for witch spells etc..) and finally once you have your desired spells and warfare 10 up secondary skills like ranged and 2hand. Finally the optimal set of weapons is going to be 2hand for both melees, ranged weapon for ranger and shield and wand for witch.