The key for me to beating this on my first run was to put the entire party on HOLD, and the moment the battle began, run all of them into the corner up against the ledge. Except for a few spear-throwing Qunari, everything else (including the saarebas) will come down the stairs and into the corner with you, allowing Aveline to taunt more effectively, and everything to be within reach of any AoE the party uses. It makes all the difference in control - I wiped 3 times trying to figure out how to manage that fight, but the first time I LoS'd them into the corner, I had little trouble.
If your PC is a rogue, save all your big hits (Assassinate, Twin Fangs, that badass duelist backstab whose name I can't remember) for when you see a mage - your rogue should be able to take them out solo on casual before they can do much (if any) damage. Focus-firing the mages is key, because while rounding up all the Qunari in the corner helps with aggro management, it also makes the entire party sitting ducks for the really nasty Tempest the mages cast.
Just a note - the one-on-one duel can be just as troublesome for a dual-wield rogue. My first run, I couldn't beat him one-on-one at all - I was assassin-specced and got nearly one-shotted any time I got within melee range. My solution for this was to spec primarily into Duelist, making sure to get all the defense bonuses from the sustained spell and the passive bonuses. I also switched out a few tanking items with Fenris before going in to the throne room, so my health pool was pretty decent. I still needed to use potions whenever they were up (stamina is really tricky during this duel too), and do some kiting, but it was all but trivial on Casual - I'm pretty sure I could beat him on at least normal taking this route.
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If your PC is a rogue, save all your big hits (Assassinate, Twin Fangs, that badass duelist backstab whose name I can't remember) for when you see a mage - your rogue should be able to take them out solo on casual before they can do much (if any) damage. Focus-firing the mages is key, because while rounding up all the Qunari in the corner helps with aggro management, it also makes the entire party sitting ducks for the really nasty Tempest the mages cast.
Just a note - the one-on-one duel can be just as troublesome for a dual-wield rogue. My first run, I couldn't beat him one-on-one at all - I was assassin-specced and got nearly one-shotted any time I got within melee range. My solution for this was to spec primarily into Duelist, making sure to get all the defense bonuses from the sustained spell and the passive bonuses. I also switched out a few tanking items with Fenris before going in to the throne room, so my health pool was pretty decent. I still needed to use potions whenever they were up (stamina is really tricky during this duel too), and do some kiting, but it was all but trivial on Casual - I'm pretty sure I could beat him on at least normal taking this route.