Avanced Marketplace Customisation / Products combination

[Gombi92]

I've bought this webkul module https://store.webkul.com/PrestaShop-Extensions/Prestashop-Advanced-Marketplace.html  and have customised it this way :
 
I've added 3 new fields to marketplace_seller_product table named:
 
- brand name
- EAN code
- peremption date
 
I've added 1 field to marketplace_seller_info named :
- department number
 
It works rather fine from front and back but now, I would like :
 
1- to pass my variable EAN code to table ps_product in order to allow my customers to instantsearch results just printing ean codes. I've tried to insert data like this in addproductprocess.php:
Db::getInstance()->execute("INSERT INTO `"._DB_PREFIX_."product` (ean13)VALUE('".$code_EAN_du_lot."')");
but the problem is that it adds 2 rows in ps_product table instead of just updating the table correctly..

 

2- to allow my customers to display all products from a single department number (=the field i've added to marketplace_seller_info table). I've tried unsuccessfully to customise a module but the combination is quite hard to achieve because datas are not stored at the right place..
 
If you've tried the same and have a solution, please help xxx
Thanks in advance