Paladin: Jenlyns goes from outright loathing the notion of being helped to readily acknowledging that the WoL is their superior, and the Sultansworn itself from being in ill-repute, to being noted as a total sham, to rebuilding its legitimacy. Solkzagyl from a disgraced thief, to dead, to... not dead but weirdly manipulative and of questionable morals. Constaint wasn't even around for ARR. You could drag in the Gladiators' Guild for them, but then Mylla goes from a woman of shaky convictions, positional legitimacy and emotional standing to a strong leader but ultimately lesser warrior, while Aldis goes from disgraced, to put to death, to a wanderer, to a masked anonymous agent, to a Samurai.
Warrior: So, there's no question you're going with Curious Gorge for the representative here. But in ARR he's a generally serious man struggling with the burden of the Inner Beast and occasionally giving in to it; in Heavensward he's basically tried to swear off Warrior-ing entirely, and in SB and ShB he takes a complete tonal swerve as the entire story becomes a rom-com. This one might be the hardest, because his entire direction shifts in a way you can't just conditionalize, and presenting one while the player is in the other will feel wrong.
Gunbreaker: Actually pretty much fine, because you're gonna be putting forward Radovan, and his character remains largely the same. You might want to also factor in Bozja progress with him, though, for some two-dimensional conditionalized dialog.
Dark Knight: Well... to summarize,
OH NO! We're basically forced to use Sidurgu, because Fray has existence problems, so already we're going with the less popular character. But Sidurgu's not in 30-50 DRK and so is a complete whiff there, and goes through some crucially important character development that would basically influence all of his dialogue over the course of HW and to a lesser extent SB. And then we have to factor in Rielle; reasonably speaking Sidurgu's not gonna leave her behind, even though he really should, and how much she respects him changes immensely over the course of the storyline.