<section>
  <div class="container">
    <div class="tabswrapper">
      <h2>Заголовок</h2>
      <p>Описание</p>
      <div class="tabs-custom tabs-vertical row no-gutters" id="tabs-1">
        <ul class="nav nav-tabs nav-custom nav-custom-tabs col-md-3">
          <li class="nav-item" role="presentation">
            <a class="nav-link active" href="#tabs-1-1" data-toggle="tab"><?php echo get_cat_name(8);?></a>
          </li>
          <?php
          $parent_id = 8;
          # получаем дочерние рубрики
          $sub_cats = get_categories( array(
            'parent' => $parent_id, # or 'child_of'
            'hide_empty' => 0
          ) );
          ?>
          <?php $counterr=2 ?>
          <?php
          if( $sub_cats ){
          foreach( $sub_cats as $cat ){
          ?>
          <li class="nav-item" role="presentation"><a class="nav-link" href="#tabs-1-<?php echo $counterr ?>" data-toggle="tab"><?php echo $cat->name ?></a></li>
          <?php $counterr++ ?>   
          <?php
          }
          wp_reset_postdata(); // сбрасываем глобальную переменную пост
          }
          ?>
        </ul>
        <div class="tab-content text-left col-md-9" style="min-height: 620px">
            <div class="tab-pane fade active show" id="tabs-1-1">
            <!-- Owl Carousel -->
            <div class="owl-carousel carousel-product" data-items="1" data-md-items="1" data-lg-items="2" data-xl-items="3" data-stage-padding="0" data-loop="true" data-margin="50" data-mouse-drag="true" data-autoplay="true" data-autoplayhoverpause="true" data-nav="true">
            <?php
              $posts = get_posts( array(
              'numberposts' => -1,
              'category'    => 8,
              'orderby'     => 'date',
              'order'       => 'DESC',
              'include'     => array(),
              'exclude'     => array(),
              'meta_key'    => '',
              'meta_value'  =>'',
              'post_type'   => 'post',
              ) );
            foreach( $posts as $post ):?>
              <h5 style="margin-bottom: 36px;"><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h5>
            <?php endforeach; ?>
            <?php  
              wp_reset_postdata(); // сброс
            ?>  
            </div>
            </div>
            <?php
            $parent_id = 8;
            # получаем дочерние рубрики
            $sub_cats = get_categories( array(
              'parent' => $parent_id, # or 'child_of'
              'hide_empty' => 0
            ) );
            ?>
            <?php $countt=2 ?>             
            <?php
            if( $sub_cats ){
            foreach( $sub_cats as $cat ){
            ?>       
            <?php
            # получаем записи из рубрики
            $myposts = get_posts( array(
              'numberposts' => -1,
              'category'    => $cat->cat_ID,
              'orderby'     => 'post_date',
              'order'       => 'DESC',
            ) );
            ?>
          <div class="tab-pane fade show" id="tabs-1-<?php echo $countt ?>">
          <!-- Owl Carousel -->
          <div class="owl-carousel carousel-product" data-items="1" data-md-items="1" data-lg-items="2" data-xl-items="3" data-stage-padding="0" data-loop="true" data-margin="50" data-mouse-drag="true" data-autoplay="true" autoplayTimeout:5000 data-autoplayhoverpause="true" data-nav="true">
            <?php $countt++ ?>  
            <?php
            # выводим записи
            global $post;
            foreach($myposts as $post){
            setup_postdata($post); ?>
            <h5 style="margin-bottom: 36px;"><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h5>
            <?php
            }
            ?>  
            </div>
          </div>

          <?php
          }
            wp_reset_postdata(); // сбрасываем глобальную переменную пост
          }
          ?>  
        </div>
      </div>
    </div>
  </div>  
</section>