Drupal and node relationships
You should be able to duplicate this functionality using the Field Collection module. 

In short, you attach a Field Collection field to an entity, and then define the Field Collection in a separate UI (/admin/structure/field-collections) by attaching additional fields to it. It will behave like (and is in fact internally represented as) a first-class entity, and the module allows you to manage these items from the same parent form you attached the Field Collection field to, complete with drag-and-drop for reordering and the like. It also has a number of other nice features, such as letting users with appropriate permissions add/edit/delete Field Collection items while viewing the parent node without having to go into the edit form itself.