Codeko

With this plugin you can set any post type (or posts types) as parent of any post type.
Urls will be wellformed, redirects will work, breadcrumbs will work fine.
This plugin is recomended when you need a url structure with a mix of post types. Any url structure you can imagine could be done.
Post types rewrite slugs will be ignored

Custom Posts Parents

Set any post type (or types) as parent of any post type. Any post structure can be created with this plugin.

alekc

Sometimes you don’t want to show parent directories in permalink because they are not really necessary or because you know that in the future your child directory will change it’s parent.
For example: 
+Work in progress 
–Site 1 
–Site 2 
+Work Finished 
–Site 3
In this case Site 3 originally have been part of “Work in progress”, and on job done it has been moved under “Work Finished”.
So if you install this plugin your link will be transformed in this way:
domain.com/parent_category/child_directory/post_name => domain.com/child_directory/post_name 
domain.com/category/parent_category => domain.com/parent_category 
domain.com/category/parent_category/child_directory => domain.com/parent_category/child_directory

Remove Parents

Remove Parents is a tiny plugin which remove "category" and parent categories from permalink.

Custom Posts Parents vs Remove Parents