Hi,
Your template seems to load some Bootstrap 3, but not Bootstrap 2. But HikaShop is, like native Joomla, supporting only Bootstrap 2 (though BS 3 support is under way, I hear).
So, turning Bootstrap off in HikaShop is the right thing to do for you. "Missing responsiveness" can then be added with custom CSS and media queries, such as
@media (max-width: 767px) {
.hikashop_products_listing .hikashop_product {width: 100% !important;}
}
for product listings such as in the page you're linking to.
In case you wonder, here is documentation on how to do so:
www.hikashop.com/support/support/documen...ize-the-display.html
More similar code may be required for other shop elements or pages, of course. But so it goes if things aren't 100% compatible out of the box, and I'm sure you'll find more support here if you need it.