plugin admin menu sub pages malfunction

I have a simple site help menu on the admin page. My plugin is site specific but while I can show the menu links the function calls dont work.
Only sub menu 1 is shown whatever subpage link selected.
Can any one help please.
My code is

<?php
/*
Plugin Name: Help
Description: Adds a site help link to the admin menu
Author: Mike Stocks
*/
//define constant plugin file name
global $wpdb, $wp_version;
define ('siteHelp',basename(__FILE__));

// mt_add_pages() is the sink function for the 'admin_menu' hook
function add_help_pages()
{
    // Add a new top-level menu:
   // The first parameter is the Page name(Site Help), second is the Menu name(Help)
   //and the number(5) is the user level that gets access
    add_menu_page('siteHelp', 'Site Help', 2, 'siteHelp', 'mt_toplevel_page');
    add_submenu_page('siteHelp','Site Help','Authors-General',2,'__FILE__','submenu_1');
    add_submenu_page('siteHelp','Site Help','Authors-Marketing',2,'__FILE__','submenu_2');
    add_submenu_page('siteHelp','Site Help','Authors-Edit',2,'__FILE__','submenu_3');

}

// mt_toplevel_page() displays the page content for the custom Test Toplevel menu
function mt_toplevel_page() {
    echo '
    <div class="wrap">
      <h2>Site Help</h2>
      <p>This page contains information and tutorials that are specific to your site.
      If you have trouble with anything on this page contact Mike Stocks of
      <a href="https://hawkesleypublishingsolutions.com">Hawkesley Publishing Solutions</a> by sending an email using the reference"[email protected]"

      <h3>Video Tutorials</h3>
      <p>Please note that these tutorials require a Flash Player, available to
      <a href="https://www.adobe.com/shockwave/download/index.cgi?P1_Prod_Version=ShockwaveFlash">
      download for free from Adobe</a>.</p>
      <ul>
        <li><a href="/wp-content/uploads/filename.swf">How to edit existing pages</a></li>
        <li><a href="/wp-content/uploads/filename.swf">How to create a new page or post</a></li>
      </ul>
    </div>
    ';
    exit;
}
function submenu_1(){
				echo "submenu 1";
				exit();
}
function submenu_2(){
				echo "submenu 2";
				exit;
}
function submenu_3(){
  				echo "submenu 3";
  				exit;
}
// Insert the add_help_pages() sink into the plugin hook list for 'admin_menu'
add_action('admin_menu', 'add_help_pages');
?>