Displaying navigation a special way, need help…

Heya,
So I’m working on this site: https://reservation-telephone-company.pivotgroupdev.com/products and when you click on a SUB item in the navigation on the left, it removes all the other navigational items displaying only the children for that page.
The problem is, I need it to display all the children of the top level parent page. So even if it’s three levels deep on the “Products” page, it’s showing all the children for the “Products” page still. I can’t seem to figure out how to accomplish that. Can someone help? Thanks!

<div class="row-2-col-1-row-1">
			<a class="voice <?php if ( is_page('voice'))  { echo 'current_page_item'; } ?>" href="<?php bloginfo('url'); ?>/voice">Voice</a>
			<a class="data <?php if ( is_page('data'))  { echo 'current_page_item'; } ?>" href="<?php bloginfo('url'); ?>/data">Data</a>
			<a class="video <?php if ( is_page('video'))  { echo 'current_page_item'; } ?>" href="<?php bloginfo('url'); ?>/video">Video</a>
			<a class="bundle <?php if ( is_page('bundle'))  { echo 'current_page_item'; } ?>" href="<?php bloginfo('url'); ?>/bundle">Bundle</a>
		</div>

		<?php
		if(is_search() || is_404()) { } else {

			// if($post->post_parent) {
			//	$children = wp_list_pages("title_li=&child_of=".$post->post_parent."&echo=0");
			// } else {
			//	$children = wp_list_pages("title_li=&child_of=".$post->ID."&echo=0");
			// }

			// if ($children) {
			echo '
				<hr />

				<div class="row-2-col-1-row-2">
					<h1>' . get_the_title($post->post_parent) . '</h1>
			';

				if ($post->post_parent == 0) {
					echo wp_list_pages('child_of=' . $post->ID . '&sort_column=post_title&title_li=');
				} else {
				 	echo wp_list_pages('child_of=' . $post->post_parent . '&sort_column=post_title&title_li=');
				}

			echo '</div>';

			// }
		}
		?>