Hi there,
the plugins you’re using to add the Author Box and the Related Posts. Check the plugin documentation they should provide a Shortcode option for adding them to your post.
You can the use a Hook Element to add the shortcodes to a page.
1. create a new Hook Element in Appearance Elements.
2. Add your 2 shortcodes to the Hook (author box then related posts ).
3. Select the hook: generate_after_content
4. Check the Execute Shortcode option.
5. Set the Display Rules to Posts all Posts.
This will display content, post meta ( post tags ), author box, related posts in that order.