А может наоборот все (fancybox в slick слайдере)?
<a href="#modal">Кнопка</a>
<div class="remodal" data-remodal-id="modal">
<button data-remodal-action="close" class="remodal-close"></button>
<h1>Remodal</h1>
<section class="regular slider">
<div>
<img src="http://placehold.it/350x300?text=1">
</div>
<div>
<img src="http://placehold.it/350x300?text=2">
</div>
<div>
<img src="http://placehold.it/350x300?text=3">
</div>
<div>
<img src="http://placehold.it/350x300?text=4">
</div>
<div>
<img src="http://placehold.it/350x300?text=5">
</div>
<div>
<img src="http://placehold.it/350x300?text=6">
</div>
</section>
<br>
<button data-remodal-action="cancel" class="remodal-cancel">Cancel</button>
<button data-remodal-action="confirm" class="remodal-confirm">OK</button>
</div>
$(document).on('opened', '.remodal', function () {
$(".regular").slick('reinit');
});
$(document).on('ready', function() {
$(".regular").slick({
dots: true,
infinite: true,
slidesToShow: 3,
slidesToScroll: 3
});
});