Display just the Post’s parent Category, not child

I want to display all post under a parent category (custom taxonomy) ONLY!.

Here’s what I’ve done so far:’

<?php
        
        $custom_taxterms = wp_get_object_terms( $post->ID, 'product_type', array('fields' => 'ids') );
        $custom_taxterms_two = wp_get_object_terms( $post->ID, 'brand', array('fields' => 'ids') );
    
            $args = array(
            'post_type' => 'product',
            'post_status' => 'publish',
            'posts_per_page' => 8,
            'orderby' => 'date',
            'order'   => 'ASC',
            'tax_query' => array(
                    'relation' => 'OR',
                    array(
                        'taxonomy' => 'product_type',
                        'field'    => 'id',
                        'terms'    => $custom_taxterms,
                        'include_children' => false
                    ),
                    array(
                        'taxonomy' => 'brand',
                        'field'    => 'id',
                        'terms'    => $custom_taxterms_two,
                        'include_children' => false
                    ),
                ),
            'post__not_in' => array ($post->ID),
            );
    $related_items = new WP_Query( $args );

?>

This displays all the posts including the sub categories, which I don’t want to.

Thanks!!