I know its an old one but it does not seem satisfactorily answered
For drupal 7 usually don't need to mess with template files for such a task.
I would use https://www.drupal.org/project/field_extractor which is a field formatter for entity reference that will let you output any referenced fields from the list of referenced entities (only 1 field though)
If you want to output more than one fields I would suggest the https://www.drupal.org/project/eva which will allow you to create a special entity reference view which you can associate with the referencing entity (parent) and will allow you to output any fields from that entity and format it any way you would format a view. Automatically the view will be available in the display settings of the referencing entity so you can change the order of appearence.
if the previous 2 modules don't seem to help you can try 1 of the following which work with views but they are a little more difficult to setup and I am not going to go into detail here
(sorry my reputation wont allow me to post more than 2 links)