In D7 I have two new node type defined e.g. branch and leaf. The branch is a collection of leaves that I'm referring to using the entity_reference module. In the picture below the leaves are the nodes representing the colors. The leaves could be re-used in several branches.
I would like to add for each of the referenced leaves, two checkboxes to add some information about that leaf that is referenced in that branch. I have added on the picture manually the checkboxes. This is what I would like to achieve. Then, programmatically when I read the branch and all its leaves, I want to be able to retrieve the checkboxes value as well. Everything is working far, I just need to know how to add the leaves, so that at edit time when I edit a branch I can tick the checkboxes as needed.
How could I do that? If there is no module that exists, which hooks should I use for adding this fields to the referred leaf node in the branch? I do not want to add new fields for the leaf node type, I need the new fields/chekboxes to be added to a branch for each leaf thus at the moment of referring to the leaf and for each leaf.