For Astarion, I prefer Bard. It makes sense with his background of enticing victims to return to Cazador with him. He strikes me as naturally performative in nature.
More than that, I can imagine him playing sad music from his violin. What else has he spent centuries doing if not concentrating on his music? A vampire playing sad, melancholy music from a lonely violin. You can't convince me that isn't appropriate.
I tend to lean toward Swords Bard, solely because of the adventure he's on. He needs to learn to fight, fast.
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For Halsin, I prefer a mixture of Bear Heart Barbarian and Moon Druid. It captures that wildness and strength I think he should bring with him.
In combat, it helps that he can rage and then turn into an actual bear, making him a perfectly resisting tank on the field.
