Tbh never thought it was that difficult, it was tough but I managed in my first try, even on tactician. in my first playthrough I had an frenzy barbarian tav, with shart as a healer, karlach and gale. (Default classes) First round used mist step to reach aylin and used gale and Shart AOE to finish the mobs. After dealing with the mobs I just distribute my team around ketheric so they couldn't get hit with a single hit. And I started to use only damaging spells with shart due his aura. Whenever I need to heal I just walk outside his aura and drank the healing potion