If you’re looking to restrict the ability to view pages or posts to those that have a specific role, you can use the method described here: https://wpti.ps/check-if-user-has-specific-role-or-capability-in-wordpress/
You could create a custom role for those that need access and then check for that role using the custom function in the link above. If going that route, I’d implement a custom post type as well specifically for that type of content, then create a template for the post type that ensures that content is always displayed with the role check.