Sort wp_query results by parent page title

I’m trying to sort an array alphabetically based on the parent page title. I have a query that retrieves all pages with a specific page template. When outputting the retrieved pages I need to sort them by the title of the parent page and not the title of the retrieved page itself.

What I have so far:

$opnamePages = new WP_Query(array(
    'post_type'         => 'page',
    'posts_per_page'    => -1,
    'post_status'       => 'publish',
    'orderby'           => 'title',
    'order'             => 'DESC',
    'meta_key'          => '_wp_page_template',
    'meta_value'        => 'templates/dienst-sub-opname-page.php'
));

if($opnamePages->have_posts()){
    echo "<div class='subNavigationDropdown'>";
        echo "<div class='dropdown'>";
            while($opnamePages->have_posts()){
                $opnamePages->the_post();
                $parentPage = wp_get_post_parent_id(get_the_ID());

                    echo "<a href='".get_permalink()."' title='Ga naar ".get_the_title()."'>".get_the_title($parentPage)."</a>";
            }
        echo "</div>";
    echo "</div>";
wp_reset_postdata();

}