How to make featherlight gallery work with custom trigger and different markup? - featherlight.js

Question

I looked at many featherlight.js posts already, but just could not work out how to make the gallery work without a tags etc.
My example is here: http://jsfiddle.net/pwLnrmoc/5/
HTML Code:
<h3>Gallery with different Markup</h3>
<p>Works fine as "single" featherlight, but not as a gallery. I do not want to introduce a tags to make this work as a gallery. What needs to change in the JS to make this work as a gallery?</p>
<ul class="gallery">
<li class="gallery__item">
<div class="buttons">
<button class="openLightbox">Open in lightbox</button>
<button class="openLightboxGallery">Open in lightbox gallery</button>
<figure class="lightboxContent">
<h3>Item 1</h3>
<img src="http://farm8.staticflickr.com/7070/6874560581_dc2b407cc0_b.jpg" />
</figure>
</div>
<img src="http://farm8.staticflickr.com/7070/6874560581_dc2b407cc0_q.jpg" />
</li>
<li class="gallery__item">
<div class="buttons">
<button class="openLightbox">Open in lightbox</button>
<button class="openLightboxGallery">Open in lightbox gallery</button>
<figure class="lightboxContent">
<h3>Item 2</h3>
<img src="http://farm5.staticflickr.com/4005/4400559493_3403152632_o.jpg" />
</figure>
</div>
<img src="http://farm5.staticflickr.com/4005/4400559493_f652202d1b_q.jpg" />
</li>
<li class="gallery__item">
<div class="buttons">
<button class="openLightbox">Open in lightbox</button>
<button class="openLightboxGallery">Open in lightbox gallery</button>
<figure class="lightboxContent">
<h3>Item 3</h3>
<img src="http://farm1.staticflickr.com/174/396673914_be9d1312b1_o.jpg" />
</figure>
</div>
<img src="http://farm1.staticflickr.com/174/396673914_be9d1312b1_q.jpg" />
</li>
</ul>
JS Code:
$(document).ready(function(){
$('.openLightbox').click( function(evt) {
const $target = $(evt.currentTarget);
const $figure = $target.siblings('figure');
console.log($figure.length);
// to open in a single slide
$.featherlight($figure);
})
$('.openLightboxGallery').click( function(evt) {
const $target = $(evt.currentTarget);
const $figures = $target.closest('.gallery').find('figure');
console.log($figures.length);
// to open in a gallery
$.featherlightGallery($figures);
})
});
It works fine with the "single" featherlight button, but not with the gallery. I do not know how to set the content filter or target in my case. That's the error: Featherlight: no content filter found (no target specified).
Ideally the way you call featherlight and featherlightGallery should be consistent and work the same way.