More multiple add to cart buttons drupal commerce
It appears that you're looking for something that is decribed in detail in Multiple products per Add To Cart form (product kits/packages) also.
And that issue is what was the inspiration for the Commerce Product Bundle module (available for D7, but only as an alfa version for now). Here is a excerpt from its project page:

You can define products that consists of other products. They are all combined in one add to cart form. The form works like the core add to cart form with all the fancy selection and ajax magic. So the customers can make their selections as usual. The difference is, that the products from mulitple reference fields were presented on one add to cart form.
The bundle is then represented by one order line item. This allows the maximum compatibility with other modules such as shipping or payment modules.