Show only some categories on a post

Hi I have a Bookshelf section on my website. I want to have posts about books and give them a category of their own i.e “Bookshelf” as the parent category and then category topics such as “self empowerment”, “Beliefs”, “Love” etc.as the next level of the hierarchy.
I have all the necessary categories set up and am also using the Display Widgets plugin… so I have it all set up to show the right menu on the right posts.

The problem is the Category Widget I have set up for Bookshelf posts is showing All the categories of all my posts in the drop down. I only want the Bookshelf Categories to show on that category menu.

Here is the link for the Bookshelf posts

http://www.marleneroseshaw.co.uk/category/bookshelf/

Here is the link for the other posts with the other, original category menu set up
http://www.marleneroseshaw.co.uk/