Document collection and documents in collection as template

Not out of the box, but perhaps via code?

Add some logic that reacts when the object is first created and create a copy of all the documents referenced by the collection-members property, then update the property with the new values.

I tried to add a Member to a Collection via Property Calculator but it doesn't get added:

I actually moved to an object type, and used property calculator to copy documents from a metadata which linked to the template documents, into another metadata, than remove that initial property that contained the templates.

I actually moved to an object type, and used property calculator to copy documents from a metadata which linked to the template documents, into another metadata, than remove that initial property that contained the templates.