We have in our import/export business in the most cases for one purchase order different suppliers (material supplier, delivery costs, inspection costs, costume and so on) and all of them have separate invoices. How can i manage all this suppliers to one purchase order? Because at the End all of this invoices should also create the final purchase price per product/unit. 

As example following:

supplier 1: Producer by which we order an amount of products

supplier 2: Logistic company which organize and do the whole delivery 

supplier 3: Packing Material, he is sending the packing material to the producer because the material is costumized

supplier 4: Import Costums, which sends also an invoice with taxes and other stuff

All of this suppliers should be together on one purchase order, because all they together create the total amount of this purchase order. Finally it should be automated that the total amount of all invoices divided by the amount of goods should create the final price of an product per unit. 

Could somebody help me, how to create such an process in Odoo 9?

Thanks a lot in advanced!