multiple image upload from frontend in wordpress

I have a CPT “Annonce” which is supposed to have four attached images. Now I building a frontend form to allow users to submit posts with four image upload fields. When I try to submit the form with multiple images, only the last image appears as featured in the dashboard. I see the other images in Media section but not in the post edit page so I can change or delete theme.

I’m using this code in page-post.php:

        if ( $_FILES ) {
        $files = $_FILES['upload_attachment'];
        foreach ($files['name'] as $key => $value) {
            if ($files['name'][$key]) {
                $file = array(
                    'name'     => $files['name'][$key],
                    'type'     => $files['type'][$key],
                    'tmp_name' => $files['tmp_name'][$key],
                    'error'    => $files['error'][$key],
                    'size'     => $files['size'][$key]
                );

                $_FILES = array("upload_attachment" => $file);

                foreach ($_FILES as $file => $array) {
                    $newupload = insert_attachment($file,$post_id);
                }
            }
        }
    }
...

<label for="postPhoto1">Photo 1 :</label>
<input type="file" name="upload_attachment[]" id="postPhoto1">

<label for="postPhoto1">Photo 2 :</label>
<input type="file" name="upload_attachment[]" id="postPhoto2">

and in functions.php I have this function:

function insert_attachment($file_handler,$post_id,$setthumb='false') {

  // check to make sure its a successful upload
  if ($_FILES[$file_handler]['error'] !== UPLOAD_ERR_OK) __return_false();

  require_once(ABSPATH . "wp-admin" . '/includes/image.php');
  require_once(ABSPATH . "wp-admin" . '/includes/file.php');
  require_once(ABSPATH . "wp-admin" . '/includes/media.php');

  $attach_id = media_handle_upload( $file_handler, $post_id );

  if ($setthumb) update_post_meta($post_id,'_thumbnail_id',$attach_id);
  return $attach_id;
}

Using this form the images are successfully uploaded but only last image get set as featured image, and I want to show other images in the post edit page too.

any help?