How to display and select multiple products

-- url of the page with the problem -- : site.elalaji.com
-- HikaShop version -- : 2.3.5
-- Joomla version -- : 3.3.6
-- PHP version -- : 5.6.3
-- Browser(s) name and version -- : Firefox 35.0.1

How to display all products under one category in table or grid format with "Add to Cart" button by multiple selection and quantity changes respectively

Hi,

In the settings of your menu/module, you can select the value "Grouped by category" for the option "Sub elements filter",
This will group the products per category, but if you want the product of only one category, select "direct sub elements".
I recommend to use the "table" display for your need.

And in Configuration > Main > Product select "Global on listing" for the option "Display the quantity field on the product page".
That option allow to have only the quantity field on each product and one an unique add to cart button.