Who is Khorshedbai and Ardeasar from Swimming Lessons and what is their importance?

In "The Paying Guests," Khorshedbai and Ardeasar are an elderly Parsi couple whose one child lives in Canada. They sublet half of the flat belonging to Kashmira and Boman. Things go well for 18 months until the landlords need the rooms back for their second child. Khorshedbai's late parrot, Pestonji, appears to her in dreams, showing her how to get even by strewing garbage on the neighboring windows, parapets, door, and inner ledge.