static $has_many = array(
'Images' => 'Image'
);

public function getCMSFields() {
$fields = parent::getCMSFields();

$manager = new HasManyFileManager(
$this,
'Images', // name -> will be used for file grouping
'Images' // relation name defined in $has_many
);

// creating tab for the "Files" Manager
$fields->addFieldToTab('Root.Content.Images', $manager);
return $fields;
}   

public function onBeforeDelete(){
parent::onBeforeDelete();
$this->deleteAttachedFiles();
}

class TeamPage extends Page {
   
   public static $db = array(
   );
   
   public static $has_one = array(
'Video' => 'File',
'PreviewImage' => 'Image'
   );

   static $has_many = array(
      'Images' => 'Image'
   );

   static $allowed_children = array(
      'TeamMemberPage',
      'SponsorPage'
   );

   public function getCMSFields() {

      $fields = parent::getCMSFields();

      $manager = new HasManyFileManager(
         $this,
         'Teams', // name -> will be used for file grouping
         'Images' // relation name defined in $has_many
      );
      
      $fields->addFieldToTab('Root.Content.Images', $manager);

    $fields->addFieldToTab("Root.Content.Video", new FileIFrameField('Video'));
    $fields->addFieldToTab("Root.Content.Video", new ImageField('PreviewImage', 'Preview Image (shown before video starts)'));

      return $fields;
   }

   /**
    * Implementation of the onBeforeDelete Method for FileManager
    */
   public function onBeforeDelete(){
      parent::onBeforeDelete();
      $this->deleteAttachedFiles();
   }

}