Multiple structure combined into one: Difficulty merging structures into a collection
Route: https://getkirby.com/docs/guide/routing
Custom page method: https://getkirby.com/docs/reference/plugins/extensions/page-methods
So:
- Create a route with a pattern of your choice.
- Either create a page method that returns the combined structure field, or create a route that return the json you need, I think the page method is probably easier.