I’ve made some progress on my issue with this following code:
<?php if ($post->post_parent || is_page ('direct-sellers') ) { ?>
<?php wp_nav_menu( array('theme_location' => 'side-menu-1' ) ); ?>
<?php } elseif ($post->post_parent || is_page ('eretailers') ) { ?>
<?php wp_nav_menu( array('theme_location' => 'side-menu-2' ) ); ?>
<?php } else ?>
but now my issue is when I am on the eretailer page and navigate to a child of eretailer is displays the side nav for direct sellers. I guess I’m not sure how to distinguish between the two parent pages effectively.