@Tych
In the novel, the twins (who is contracted to Kygras by the guild) actually did say that Rude did nothing wrong and acknowledged his skills when Kygras kicked Rude out in the first chapter. In the novel, the rebuke against Kygras in the dungeon was also supposed to be said by one of the twins, not Nin.
I'm guessing the mangaka didn't want to put as much emphasis on the twins and try to develop Nin's affection meter with the readers instead. Probably because the twins are not supposed to be a romantic interest.
In the novel, right after the last dungeon failure, one of the twins couldn't take it anymore and rebuked Kygras, told him his faults and how Rude was the reason they were able to overcome the dungeon. And when Kygras blamed the two new hires instead, the twin said they did nothing wrong and did their jobs well, and that it was Kygras who was harming the entire party. The twins later left the party to go home to eat delicious food and maybe find a new party.
In the novel, they simply left, I don't remember if there was a mention that they couldn't leave because of the guild, but they left him first, before Nin.