Is it possible to increase the thumbnails size on the slide to fit the whole width of the big one? I mean, if I set it to 7 posts it is ok, but if I set it to 5 the thumbnails are the same size but it shows a blank on the right.
I guess the slider that you mean is the Slider 1, right? If yes, unfortunately, we don’t have an option yet to control that. But you can achieve that by doing some changes in there.
Please try to replace the content of this file /jnews/assets/js/jquery.jowlslider.js with this one https://pastebin.com/y021i7bN. After that, please clear all cache data on your server and on the current browser that you use.