I am assuming you are using K2 Studio. The answer is slightly different for Designer.

You seem to have solved for creating the role and adding users but need to be able to assign a task to this group of users where the all must complete before it moves on to the next task.

• In the activity that holds the task, double click on the package icon in upper left corner.

• Select the people icon,

• You normally have to click back and select advanced

• You should see Destination Rules Options, Select either "All at Once" or "One at a time" under plan for destination

• Click next and select "Create a slot for each Destination" and "Resolve all roles and groups to users"

• If you have a destination set already edit this and put in your role and select group as the type

• You also need to check your outcome rules and make sure they are "all slots of action result" and not just one slot

This will asssign the task and make sure that everyone completes it before moving to next task

I hope I understood your question on using roles and this helps. I can’t help but question if you have a list of users to create the role why you don’t just assign the task without creating the role. What brings you to using a role?