Remove parent page templates from dropdown option in child theme pages

unset-parent-page-templates.php

<?php
/**
 * Removes parent theme page templates from the dropdown option on add new/edit page screen.
 *
 * Note that the path/to/ is from the parent theme directory, so if the page templates are in a subdirectory add that path,
 *	otherwise it can be written as 'page-template.php'
 *
 * @author Joshua David Nelson, josh@jdn.im
 */

add_filter( 'theme_page_templates', 'jdn_remove_page_templates' );
function jdn_remove_page_templates( $templates ) {

	unset( $templates['path/to/page-template1.php'] );
	unset( $templates['path/to/page-template2.php'] );
	unset( $templates['path/to/page-template3.php'] );
	unset( $templates['path/to/page-template4.php'] );

	return $templates;
}