Problem finding UpdateCart function for checkout cart.

-- HikaShop version -- : 2.6.3
-- Joomla version -- : 3.6.5

Good day, I have a problem removing items in the checkout cart of Hikashop (version 2.6.3).
I know that my version is not tle latest, but every other thing is working so I wanted to fix this before editing again everything.
A Little intro:
In my site I sell bike races photos, so I have done some modifications that allow the user to buy all his photos in one click, with a fixed price.
The result is a cart with an item with a price > than 0€ and the single photos (connected to the previous item) with 0€ value.
My aim is to delete all 0€ value items when I delete (from cart) the parent item.

In the module cart (/com_hikashop/views/product/tmpl/cart.php) everything is working. I edited the function updateCart in /com_hikashop/controllers/product.php, now it updates not only a single product but an array of products.

The problem is in the checkout cart: /com_hikashop/views/checkout/tmpl/cart.php.
The remove button, only removes the main item and not the children.
From the url of the button I noticed that it operates on product_ids and not on cart_product_ids like the module cart. I double checked the function updateCart and my modification is also reproduced for product ids.

I am using firebug to debug my code, and the logs never print when I fire the button in checkout cart, while it works when I use module button.
I also noticed that if I delete the function updateCart (with some items already in the cart) in /com_hikashop/controllers/product.php the module cart stops working, but checkout cart still works.

The problem seems to be that I have edited the wrong function and there must be another updateCart () somewhere, but I cannot find it.
I tried searching the function updatecart in all the files of the hickashop component folder, but the only one is in product.php.
Is there another place in which I have to reproduce my modifications?

Thank you very much for your help, I hope my explanation is clear enough, I am not a good php developer I do it mainly for fun.

Hi,

Why not putting the other products as "options" of the main one ?
Thanks to the setting "group options" in HikaShop you will then let the core manage the link between the product and his options.

Regards,

Thank you for your answer,
maily because I have already thousand of photos. The offer package is a recent need and I don't want to reload everithing if possible.
By the way, using options I have to create a specific parent product for each racer. With my changes the customer can buy everything that appear after filtering the race on the base of his number.
You gave me a good starting point, I will check how the option removal works, thank you!