Hi @huwrowlands
I’m afraid this structure needs you to edit your permalink settings on “Settings > Permalinks”:
http://www.domain.com/listings/post-id-number/france/barcelona/.
For the second link structure, i believe you can use acf/save_post hook to do it.
You can use wp_update_post() function based on the custom field. Be caution with the infinite loop, though. This page should give you more idea about it: https://codex.wordpress.org/Function_Reference/wp_update_post#Caution_-_Infinite_loop.
I hope this helps.
