First, just checking I've understood the problem correctly (please correct me if wrong):
- You have a page set up using panels, on which you want to display a node and that node's child nodes.
- You want a list of child nodes that is configurable. Mini panels don't work well for as the number of child nodes can vary.
- Panels is essential, Inline Entity Form is not necessarily essential but is the best option you've found so far for giving nodes child nodes
If this is right, I wonder if you couldn't get what you want using Context Views in panels that use relationships from Relation module (or Entity Reference might do the job more simply - Inline Entity Form might work the same way too but I don't know how well it integrates with Views). After all, lists of any number of items from one relationship with configurable fields is something Views is designed for, and using a context view allows you to chop the view up in Panels and place each part of the view in a way that suits your layout:
- Create a directional relation type between the appropriate node types - let's call it 'Is child of' (or, add an entity reference field to the parent node content type)
- Create a view block showing content and give it a Context display ( context displays are a display type along the top like Page, Block...)
- Give it a contextual filter for the Nid of the parent node, and a required relationship using the entity reference or relation to get the referred child node (if it doesn't work first time, the last time I used relation with views you had to chain node>relation and relation>node relationships to get the other node. Direct node>node relationships didn't work. Might be fixed by now)
- Add and configure your fields however you want them in Views, using the 'Is child of' relationship for each of them
- In Panels, load the view as context on the Panels Context page (make sure the view's contextual filter gets the nid somehow)
- In Panels Content page, you'll find the elements of your view under View Context. You can place all rows (each row being one child node), individual rows or row ranges, and header, footer, exposed filters etc whereever you like in your panels layout.
The individual fields within each 'embedded' child node are controlled in Views - which has all the flexibility of Panels plus extra features for rewriting, tailoring and combining individual fields - and the display between the child nodes and each other and other page elements is controlled in Panels.
If you choose Relation, you can also add fields to the linking relation itself, which can be included in each row of the view. I believe you could also have one multiple endpoint relation where one parent has several children on the same relation entity sharing the same relation fields. Not sure if they've got those cases working with Views yet, though. Entity Reference is less powerful, but simpler.