don't sweat the offhand too much for now, Think of it basically like a stat-stick that gives your mainhand an extra attack because you can only ever have 1 extra attack from the offhand but the APR bonus always applies to the main. Once you level more it'll just be gravy, just be patient for the pip levels to come in. Chapter 2-4 are just easy anyway. Just get 2 pips into TWF so there's no mainhand penalty and fill the rest in later

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As for keldorn, yeah you basically have to practice launching his innate dispel ahead of the party when you see enemies throwing up their defenses so you don't dispel yourself, but it only takes a little bit of attention. Try toggling your AI off for a couple seconds so everyone doesn't rush in first, his dispel is basically insta-cast, and then send the buffed boys and girls in. Let your mage use targeted removals like Breach etc after that.