We have used a "Role Manager" plugin with a team of authors working on the same site. It limits what they can do to their own stuff more or less. Pretty powerful.
It looks like the latest iteration is now called "WordPress Capabilities Manager", and you can find it in the WordPress repository.
Very powerful... but I don't know if it will allow specific block updates like you asked about. Maybe a solution would be for you to use an "include" type section (code it into the functions.php, call with a [shortcode] or custom field) within a post, that includes postid=xx (create a post, assign to user, replace xx with the id)