Task assignment when a SharePoint group is the destination set

I created a process in K2 for Visual Studio and specified a SharePoint group as the destination set, however when the task is created, the "Assigned To" field is empty. There is a single user in the group.

My desired result is that :

1. 
   
2. A single task be created
   
3. The "Assigned To" field be populated with the name of the group
   
4. Each user receives an email for the task.
   
5. Only a single user needs to complete the task.
   

I tried varying settings for the "Destination Rule Options", which I have to admit is not very clear to me. I end up with either the task being assigned to the single user in the group - or no one at all.

Any advice on how to achieve this ?