You want to add the title to the response, not replace the response with the title. Like this:
<?php
function get_all_images($post_id=0, $size="bigger", $attributes="") {
$post_id = $_POST['post_id'];
if ($post_id<1) $postid = get_the_ID();
if ($images = get_children(array(
'post_parent' => $post_id,
'post_type' => 'attachment',
'numberposts' => -1,
'orderby' => 'menu_order',
'post_mime_type' => 'image',)))
$title = get_the_title($post_id);
$response="<h2 class="titles">".$title.'</h2>';
foreach($images as $image) {
$attachment=wp_get_attachment_image_src($image->ID, $size);
$tranparent=get_template_directory_uri();
$response .= '<img src="'.$tranparent.'/images/transparent.gif" data-original="'.$attachment[0].'" alt="" class="imarge" />';
}
die( json_encode( $response ) );
}?>
Update
Corrected to add it before the loop.