Support Third Hierarchy Level in Parent-Child Listings (Grandparent Listings)

Problem Statement:

• Hospitable's parent-child feature only supports two levels of hierarchy (one parent with multiple children)
• Users cannot create a third level where parent properties (each with their own children) are merged under a main parent listing
• This limits the ability to offer combined bookings across multiple properties as a single unit

Current Workaround:

• Users can create separate parent-child groups (e.g., Parent A with children 1+2, Parent B with children 3+4)
• However, there's no way to merge these parent groups into a single "grandparent" listing that guests can book together

Impact:

• Hosts with multiple properties cannot offer a unified booking experience across all their properties
• Guests must book each parent group separately, which is inconvenient and may reduce booking conversion
• Hosts lose the ability to market their entire portfolio as a single accommodation option

Proposed Solution:

• Extend the parent-child hierarchy to support three levels: a main parent listing with child parent listings, each of which can have their own child properties
• This would allow hosts to create a "grandparent" listing that encompasses multiple parent groups

Unlock:

• Hosts could offer combined bookings across all their properties as a single listing
• Guests would have the option to book the entire portfolio as one unit
• Hosts could better market their multi-property offerings and increase booking value