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.

JS Morisset

If no featured image has been selected for a post, page, or custom post type, this plugin will assign the first featured image found from its parent, grand-parent, great-grand-parent, etc.
The plugin makes no permanent changes – simply deactivate the plugin to disable the automatically inherited images. 😉
<h3>Coded for Performance</h3>
This plugin uses the WordPress <code>wp_cache_get()</code> and <code>update_meta_cache()</code> functions for maximum performance and fully integrate with WordPress core functionality.

JSM Inherit Parent Featured Image

Inherit the featured image from the Post, Page, or Custom Post Type parent, grand-parent, great-grand-parent, etc.

Custom Posts Parents vs JSM Inherit Parent Featured Image