Synced Sliders. See the synced sliders demo at http://kenwheeler.github.io/slick/ This assumes Advanced Custom Fields repeater is being used, but the concept should work with any data source. Be sure to change out the field names and class names as needed.

acf-slick-synced-slider.php

<?php
/*
 * Synced sliders,
 * 
 * See the synced sliders example at http://kenwheeler.github.io/slick/
 */


// Make sure there's stuff to display
if ( have_rows( 'add_testimonials' ) ) :
  // We'll hold our slides here.
  $testimonials = [];

  // We need to populate 2 separate sliders with info from the same
  // data set. We'll run have_rows() here, stash the results in an
  // array, and then use 2 foreach loops to build the markup. This
  // makes the markup a little cleaner and avoids running have_rows()
  // twice to retrieve the same information.
  while ( have_rows( 'add_testimonials' ) ) : the_row();
    
    $testimonial['name']    = get_sub_field( 'testimonial_name' );
    $testimonial['title']   = get_sub_field( 'testimonial_title' );
    $testimonial['copy']    = get_sub_field( 'testimonial_copy' );
    $imageArray             = get_sub_field( 'testimonial_image' );
    $testimonial['img_url'] = $imageArray['url'];
    $testimonial['img_alt'] = $imageArray['alt'];

    $testimonials[] = $testimonial;

  endwhile;
  ?>
  <section class="module module-testimonials">
    <div id="<?= $id; ?>" class="container">
      <div class="testimonial-wrap row">

        <div class="col-sm-6 testimonial-content testimonial-images">
          <?php foreach ( $testimonials as $testimonial ) : ?>
            <img class="img-responsive" src="<?= $testimonial['img_url']; ?>" alt="<?= $testimonial['img_alt']; ?>">
          <?php endforeach; ?>
        </div>

        <div class="col-sm-6 testimonial-content testimonial-copy">
          <?php foreach ( $testimonials as $testimonial ) : ?>
            <blockquote>
              <?= $testimonial['copy'] ?>
              <footer>
                <cite><?= $testimonial['name']; ?>
                  <small><?= $testimonial['title']; ?></small>
                </cite>
              </footer>
            </blockquote>
          <?php endforeach; ?>
        </div>

      </div>
    </div>
  </section>
<?php endif; // end if have rows

acf-slick-synced-sliders.js

// Assumes slick is already installed.
$('.testimonial-images').slick({
  slidesToShow: 1,
  slidesToScroll: 1,
  arrows: false,
  fade: true,
  asNavFor: '.testimonial-copy'
});
$('.testimonial-copy').slick({
  slidesToShow: 1,
  slidesToScroll: 1,
  asNavFor: '.testimonial-images',
  focusOnSelect: true
});