PHP Call Parent Thumbnail

I’m currently working on my own theme, I only have it locally sadly.

Basically in the header I have a the navigation and then the featured image of the page, then a second navigation menu

———- Nav ——–
—– Feature Image —–
——– 2nd Nav ——–

I want only the parent pages to have featured images, and so the on a child page the feature image should be the same as it’s parent,

this is my code

<?php
   if ( is_page('home')) {
     echo '<div style="float: left;">';
     echo riva_slider_pro( 1 );
     echo '</div>';
} else if (is_page('our-clients' || 'our-services' || 'about' || 'our-team' || 'our-sectors' || 'information' || 'partners' || 'contact-us')) {
     echo '<div style="height: 170px;">';
     echo get_the_post_thumbnail($page->ID, 'full');
     echo '</div>';
} else  {
     echo '<div style="height: 170px;">';
     echo get_the_post_thumbnail($post->post_parent, 'full');
     echo '</div>';
 }
?>

Individually each piece works fine, but all together I can’t get the child pages to pull the same featured image as the parent. Am I missing something simple?

Thanks