Custom user roles for access to specific parts of the site

You could create a new role, say staff, and add the users you want to that specific role. Then link that role a new capability of your choice, e.g. access_staff.

Now you have a new role with a new capability, so all you need to do to restrict the access to any part of the site is add this piece of code:

if ( is_user_logged_in() && current_user_can( 'access_staff' ) ) {
    // Section
} else {
    // Let them know they don't have enough privileges or...
    wp_redirect( wp_login_url( get_permalink() ) ); // Send them to the login page 
}