Wait what the.. alright, lets ignore ethics here and think about the laws within this kingdom, if those guys do had a valid contract and their signatures that they would accept becoming slaves then that is it, there is nothing that they can do about it, just because the girls made a contract with this guy it doesn't automatically imply he is legally responsible for them.
As such, if they had used Alan nobility title they could claim the girls were criminals that attempted to rob the subjects under a noble and the penalty for their crimes is serving them or death, and paying this guy to release the boy and compensate him for breach of his contract, or threatening that disobeying nobility have repercussions to blackmail him to do so.
Anyway, thank you for the translation.