Drupal commerce "family group"
I think what you are talking about is the concept of product variations introduced by Commerce Kickstart 2.0.  Product variations allow you to group together commerce products based on choices like size and color and price.  So for example say you create a Product Variation Type called T-Shirt.   You can group together the different sizes.  

There are a few ways to get this done.  You can install Commerce Kickstart 2 and follow their tutorials.

You can install their stand alone module called commerce_backoffice and its dependencies.  I recommend the book Getting Started With Drupal Commerce by Richard Jones for an explanation of how to use back office.

As a note, I started out trying to get all of the functionality I wanted from the stand alone, but found that it was better to use Commerce Kickstart 2.0