entermix

$date = '2003-08-12';
echo (new IntlDateFormatter('ru_RU', null, null, null, null, 'd MMM Y'))
      ->format(new DateTime($date));

<?php foreach( $mainpost as $i => $post ) { ?>
    <?php if ($i == 1): ?>
        <div class="row">
    <?php endif; ?>
    <?php if ($i == 0): ?>
        <div class="col-12">
    <?php else: ?>
        <div class="col-8">
    <?php endif; ?>
        <?php the_post_thumbnail(); ?>
    </div>
<?php } ?>

</div>

<div class="row">
    <div class="col-12">
        <?php foreach( $mainpost as $i => $post ): if ($i == 0):?>
            <?php the_post_thumbnail(); break; ?>
        <?php endif; endforeach; ?>
    </div>
</div>
<div class="col-8">
    <?php foreach( $mainpost as $i => $post ): if ($i > 0): ?>
        <?php the_post_thumbnail(); ?>
    <?php endif; endforeach; ?>
</div>

Хорошо бы со схемами, расчетами, чертежами...

SELECT `p`.`product_id`, `p2s`.`price`
  FROM `product` AS `p`
  JOIN (
    SELECT `product_id`, MIN(`price`) AS `min_price`
      FROM `product_to_supplier`
      WHERE `price` > 0 AND `quantity` > 0
      GROUP BY `product_id`
  ) AS `p2s` ON `p2s`.`product_id` = `p`.`product_id`
  WHERE `p`.`status` = '1' AND `p`.`date_available` <= NOW() 
    AND `p`.`manufacturer_id` = '5011' 
  ORDER BY `p`.`sort_order` ASC, LCASE(`p`.`name`) ASC
  LIMIT 0,15