Adding "add to cart" buttons in the listing of products can be achieve with the corresponding option in the module/menu listing your products.
However, that will add the main product in the cart.
There is no option to display the characteristics selection in the listing of products. The data isn't loaded nor parsed in the listing. If you want to do it you will need to edit the listing files of the product view and add SQL query, parsing of the variant/characteristics data and the code displaying the characteristics selection and the variant display... It's a lot of work and would require to carefully analyze the code we used on the product page.
In your case, and using hikashop, I would rather not have the characteristic selection and just have a quantity field so that the customer can order several times the same 50g product.