Most galleries that I’m familiar with use a single large image primarily but some can be adjusted easier than others to accommodate what you are looking for. Though I’m not familiar with Galleriffic
https://www.twospy.com/galleriffic/
when I briefly look at it’s suggested construct shown below, I see the main larger image is pulled from the href value of the a tag. This doesn’t seem to lend itself easily to doing what you’re asking for.
<div id="thumbs">
<ul class="thumbs noscript">
<li>
<a class="thumb" name="optionalCustomIdentifier" href="path/to/slide" title="your image title">
<img src="path/to/thumbnail" alt="your image title again for graceful degradation" />
</a>
<div class="caption">
(Any html can go here)
</div>
</li>
... (repeat for every image in the gallery)
</ul>
</div>

I’ve personally been more impressed with https://spaceforaname.com/galleryview
This will allow you to have multiple bigger versions linked from a single image in the film strip. Just make sure the images are the right size.

Another work around might be to construct multiple images into one image.

Abraham