Captions in TinyMCE

Hello everyone !

I’m currently customizing the captions for a client, and I have two separate problems that I can’t seem to find a fix for.
#1 : I’m bypassing the standard WP caption shortcode in order to display the description of the media alongside the actual caption. I do that with the following filter :

add_filter('img_caption_shortcode', 'ffap_img_caption_shortcode', 10, 3);
function ffap_img_caption_shortcode($val, $attr, $content = null) {

  extract(shortcode_atts(array(
    'id'    => '',
    'align' => 'alignnone',
    'width' => '',
    'caption' => ''
  ), $attr));

  if ( 1 > (int) $width || empty($caption) ) return $content;

  // Grab ID to query post_content [description] field for image
  preg_match('/([\d]+)/', $id, $matches);

  // get the description html
  $description_html = '';
  if ( $matches[0] ) {
    global $wpdb;
    $custom_description = $wpdb->get_row("SELECT post_content FROM $wpdb->posts WHERE ID = {$matches[0]};");
    if ($custom_description->post_content) {
      $description_html = "<p class=\"caption--description\">{$custom_description->post_content}</p>";
    }
  }

  // get the caption html and other fragments for the attachement
  $caption_html = "<p class=\"wp-caption-text\">{$caption}</p>";
  $id_html      = esc_attr($id);
  $align_html 	= esc_attr($align);
  $style_html 	= sprintf('width: %s px', 10 + (int)$width);
  $content_html = do_shortcode($content);

  return "<figure id=\"{$id_html}\" class=\"caption {$align_html}\">{$content_html}<figcaption>{$caption_html}{$description_html}</figcaption></figure>";
}

That works perfectly fine, on the front end. However in the TinyMCE in the backend, the caption displays as usual. My client would get confused and so I would like to be able to see that description with the caption in the back end also. Any way that’s possible ?

And then problem #2. When editing an image in the backend’s visual editor using this button :
https://www.dropbox.com/s/rms3e7q240o0ovn/Capture%20d%27%C3%A9cran%202015-10-21%2014.40.05.png?dl=0 The opening pop up window does not allow for a quick modification of that description, only the caption. Any way I could add the description to that window ?

Thanks for any help !