Howdy Annie!
It’s nice to meet you. I would certainly like to help.
In examining your site I have found some discrepancies between this CSS file:
http://www.in8motion.com/wp-content/plugins/the-events-calendar/resources/tribe-events-full.min.css?ver=3.9.1
And the one distributed with our plugin. What this means is the file has been directly modified. One of the things I noticed that is modified is line 1287:
  /*right: 16.66667%; modificato da favrizio*/
One of your developers commented out that line undoubtedly for a reason. But, in so doing they have broken the responsiveness. You will need to consult with them on why that modification was made, and if it possible to undo it so as to fix the site. Just a friendly tip, you really should not modify those files directly. Our themer’s guide walks you through creating overrides for things like CSS. If you modify the files like is currently done, then you can not update the plugin without undoing all of your modifications. But, if you create an override as outlined in that guide, then you can freely update the plugin.
Did that all make sense? Are you able to fix this now? Please let me know, I’d love to help.
Cheers!
– Brook