Want to remove user access of default page of Courses, Events, Teachers

You can edit the posts and make change their status from Publish to Draft so no one in public can access them. While you would be able to use them whenever you want. There is no other way. 

While you have not linked the Custom post Archive pages into the navigation or any other places, but they work to handle the Post groups and archive pages this is the default way WordPress posts work as. 

Here are couple of similar questions you can explore they might help you to know how you can disable custom post type archive pages. 

https://wordpress.stackexchange.com/questions/216197/how-can-we-disable-a-custom-post-type-archive-page-but-enable-its-feed

https://wordpress.stackexchange.com/questions/216197/how-can-we-disable-a-custom-post-type-archive-page-but-enable-its-feed