what would happen if all responded but the responses were different?  i.e. 2 chose Approve and 3 chose Approval Authority not required?  How would you deal with that?

That's okay, we just want to record the outcome of each task regardless of how they responded.  As soon as all respond, workflow completes and that's it!

so there is no branching logic - i.e. do this if "Approved" and do something else if "Approval Authority not required"?

Correct, it's just to gather acknowledgement.

OK so I just had a (very quick) play.

• I added an "Assign to-do task" to a SharePoint group and checked "Create individual tasks for all group members"
• Chose All must respond
• Created a new content type called "Document Review Task"
• Published my workflow
• Navigated to workflow tasks list > list settings > edited content type "Document Review Task"
• Added a new column called "Review Outcome" as choice with your two outcomes
• Re-published workflow (not sure if required)
• Ran workflow.  All members were assigned a task to complete and in the task was the "Review Outcome" to choose.

Thanks Cassy for your detailed steps.  That did the trick!  I opted to go with the Review Task action since it allowed me to modify the task form and make it more presentable.

Once again Nintex Support to the rescue!