Instead of using document.ready()
, which loads when the HTML has been loaded, you could try using window.onload, which occurs after all the elements on the page have been loaded.
$(window).on("load", function(){
$(".fancybox").fancybox();
});
Then, if you want to load the galleries on a click event:
$('relevantIDHere').on('click', function(){
Galleria.loadTheme('galleria/themes/classic/galleria.classic.min.js');
Galleria.run('#gallery-1,#gallery-2,#gallery-3,#gallery-4,#gallery-5,#gallery-6,#gallery-7,#gallery-8,#gallery-9,#gallery-10,#gallery-11,#gallery-12,#gallery-1b,#gallery-2b,#gallery-3b,#gallery-4b');
});