Copy Related Post & Attachments

Hello @mobetman2,
you can use the actions provided by Yoast Duplicate Post for that purpose.

For example, you can hook to the dp_duplicate_post action (or dp_duplicate_page if the post type is hierarchical, like the pages) to execute a function just after the post has been saved in the wp_posts table.
You can find the docs here:

• https://developer.yoast.com/duplicate-post/filters-actions#dp_duplicate_post
• https://developer.yoast.com/duplicate-post/filters-actions#dp_duplicate_page

Actually, you can look at the plugin’s code (namely duplicate-post-admin.php) to see how the hooks can be used, since the functions that copy the taxonomies, the comments, the custem fields etc. are hooked to those actions.
You can also look at compat/duplicate-post-wpml.php to see how WPML translations are copied when the original post is cloned, again using the hooks mentioned above.

I hope this helps!