Have you tried with the review task on that eform. when you create the review task on the eform you also have to go to the advanced task details and set the reviewer can edit option to yes.
I know that the review name on the task might just confuse the end user but that should be handed through training and proper task description. Once you have created this task and proper groups assignment for access is done you should be a good to use this as a workaround as there exists no better way of handling dforms for the said purpose.
Did you enter the group as editors of the form? Contact Support and they should be able to assist.