How to Creat Item Relationship?

Dear Experts,

We have a 3 items which contain in separate bottle (Packing Item), When selecting Main item for sale order bottles also need to be updated but not included in sales order. Please Explain the relation ship we need to create for this kind of scenario.

I use below example to explain my scenario further,

Lets Imagine we maintain two items call A and B, A is the item which included in sales order but B also issued in stock with A and not invoiced. However quantities of  A&B equal at each time.

Base on above scenario we need to generate followings for our client,