If this is an excerpt from a story, I wouldn’t be of much help. But from a layman's perspective, it seems like the character is attempting to please the failed humorist or he or she would have been frank. This in turn may have triggered a chain reaction, prompting the humorist to continue with his jokes which would have further affected the character. He or she is also giving the former a false sense of happiness and appreciation.
This passage may not affect the whole story in a remarkably discernible manner, but it definitely proves the character's penchant for politeness. And that may be be a deciding factor in his or her further decisions that ultimately define the plot of the story.
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Third person plural pronoun is THEY.
If you want to create a possessive pronoun out of that one, that would be THEIRS.
Possessive pronouns, as the name itself says, determine some kind of possession. For example:
Is this books yours? - No, it's theirs.