Hi,
The products listing carousel already switches to 2 elements for some screen widths:
i.imgur.com/di18Mry.png
How to decide when to display one product or two or the number of products you configured in the module depends on the code:
if($options['dots']) {
$options['responsive'] = '{0:{items:1, slideBy:1, dotsEach: 1}, 768:{items:2, slideBy:'.$slideByFor2.', dotsEach: '.$slideByFor2.'}, 992:{items:'.$products.', dotsEach: '.$products.'}}';
} else {
$options['responsive'] = '{0:{items:1, slideBy:1}, 768:{items:2, slideBy:'.$slideByFor2.'}, 992:{items:'.$products.'}}';
}
in the file product / carousel you can edit via the menu Display>Views.
As you can read in that code, it will switch to 2 products between a width of 768 and 992px available.
So you can tweak these values there to adapt to your needs, the size of your thumbnails, etc.
For example, if you change 768 by 1, it will always display 2 products on mobile devices but the carousel might go outside of the page's width. So you need to do some tests.