Hierarchical categories

I have a hierarchical category structure with 3 levels.

On the frontend Add Listing page, I only want users to be able to select leaf categories (i.e. categories with no children). How can that be achieved?

Also I would like the selected categories to show their parent categories to help the user understand what they have selected.

For example, if the taxonomy is:

Category A
– Red
— Square
— Triangle
– Blue
— Square
— Triangle

Then I want user to be able to select Square and Triangle but not Category A, Red or Blue.

When the user has selected Square, it just shows that as “–Square” but I want it to show Category A > Red > Square so they know exactly what they have chosen.

This is for a CPT called Listings, but I don’t believe that affects the way the categories are working so I thought it best to post it in the Core support board.

Thanks!