Let me explain:

Titans are immune to spells that affect the mind (you already know that), but this immunity is removed if you put on Sandro's cloak before the battle. As long as you are wearing it, the enemy soldiers' immunity to mind-affecting spells will not work. This way, you can control the titans using the "Dominate" (Mind Control) spell. If you don't have this spell for some reason... well... then you don't!:D

Regarding the next post: feel free to ask!;)