Thanks for the update, Adriano.
You've managed to display post type B inside post type A, but because we're using one post type for our project (in order to achieve the hierarchical URL structure) that method doesn't quite fit our desired outcome.
We're hoping to display the 'child' posts of the main post type in the respective 'parent' posts of the main post type.
I hope that makes sense! Let me know if you need a more detailed explanation via email as it's a private site.
Thanks for your help.