I've had the same (three Sorcerers), you've just got to hope for the best.

I usually don't go into this battle without (a) full health; (b) full mana; (c) no wait time on the Mend ability; and (d) a blessing from Aryth's Spire.

Three Finishing Blows delivered to a single Sorcerer as soon as the battle starts will knock that Sorcerer out or, if not, get you pretty close to it. You then just need to knock each of them down systematically, use Mend when Health drops below 75% and heal with Potions every second turn if you're taking a real battering.

They take a lot of damage so if you can withstand their attacks, they're easier to knock out than the others.

Edit: Just to add, the best blessing from Aryth's Spire for this battle I've found to be the 30% mitigation one as you don't take quite the same amount of damage. The 30% increase to damage would also be helpful as you'd finish the battle quicker. The additional health each turn isn't to be sniffed at but the Sorcerers probably do more damage than you'd be gaining in health so not the best.

I just thought just treat it like how you would with three knights!

SO what I did was to blast through the middle and then defeat them from the inside out. I managed and actually beat them for the first time yesterday along with beating the main bosses Vierna Da'Sheer and her shade with ease. Which was surprising but I'm glad that I finished that "Forsaken" Dungeon and Vopar all in the same day!

When it comes to 3 of anything (or two and one of anything), order doesn't really matter. Just pick one and focus on it til its dead, and then the other one until its dead, and so on. :) Grats on making it through!

Is it easier to take out the assassins or warlords in the sub-boss three?

Assassins, imo.

Assassins pose more of a threat at the cost of having less health/defense.
Warlords are kinda tanky in comparison, but they don't hurt as much as assassins, who can potentially hit all three of your party pets with one move.

Thanks! I'll try that, cause I've always tried taking out the warlords...

One thing I've noticed with Vierna is that you can block on the same turn she uses her Mana Transfusion, and the 10 mana for the block are spent before she takes the pet's mana. I'm not sure why, because that's not true for any other move that costs mana. That gives you a lot more flexibility about when you can heal.

Does anyone have any idea how meany waves there are in the arena fight?

7th post on the first page indicates that there are 38 enemies total for the arena. A handful of 1 star, 2 star and 3 star, two 4 star and the boss at the very end.

ok thanks