There was this issue, I’m not sure if it would help you:
Basically, I had this similar problem and the way to have multiple documents to an entity instance is to create another entity Document which will have MANY-TO-ONE or MANY-TO-MANY relation with the predefined entity class FileDescriptor and the Document also have MANY-TO-ONE relation with the entity that needs to be linked with the documents. Also don’t forget to add ONE-TO-MANY relation in the entity is linked with the documents.
Then what I suppose you would need for the edit view is a nested datasource of the documents, so that you could use a multi file upload field to associate the appropriate files to it.