In a list of terms show the posts in a current term next to it(current term)

With this code parent term page lists all the child terms and the child term page lists all of the posts in current term, and the single page lists a big flat list of terms(hierarchical).

Now,

The parent term page is fine.

When it’s child term page, i want to list all child terms( not showing with this code ) + the posts in current term( showing ).

And when it’s single post, i want to list the same as child term page.

$term = get_queried_object();
        $tax = 'ntp_package_type';
        $parents = $term->parent;
        $term_id = $term->term_id;

        if($parents == 0){
            wp_list_categories( array (
                            'taxonomy'  => 'ntp_package_type',
                            'pad_counts'=> 0,
                            'title_li'  => '',
                            'child_of'  => $term_id,
                            )
            );
        }
        elseif (is_tax($tax, $term->name)){

            $args = array(
                    'post_type' => 'ntp_package',
                    $tax => $term->name,
            );
            $wp_query = new WP_Query($args);
            if( $wp_query->have_posts() ):
            while ( $wp_query->have_posts() ) : $wp_query->the_post();
            echo "<p><a>".$post->post_title."</a></p>";
            endwhile;
            endif;

        }
        elseif (is_single()){

        }

It is for a sidebar sub nav. is it a right way to do? I’d really appreciate any help.