How to view and edit a relationship between nodes?

I'm going to explain de situation first:

I have 2 entities, then i have a composition relationship between them, Entities B are part of entity A.
In drupal I just have 2 node types. Node A and Nodes B. I create first the node A. then What to do with the creation of nodes B?

I guess the best way to relate them is that B nodes have a reference to node A. But then, how to create the B nodes?

Option 1. create it by 'create content', and set the reference to node A.
Option 2. create it from editing page of node A.

In option 1 I dont know how to show the B nodes in the page of Node A. There's a way to set custom PHP on the nodes A to show what i want as i want?

In Option 2, there's a way to create new nodes (B) while you are editing a node (A).

I think im missing something coz it seems usefull to be able to customize a part of a Node, puting a panel on it or just your own PHP code.

Thanks in advance.

Marry Christmas to everybody!