the conch symbolizes the wildness of their environment.
this should be right correct me if i'm wrong.
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.
A) to analyse the theme in a piece of narrative writing