You can use the Subtask To Group Plugin to easily duplicate a task for a group of users.

It uses a regular sub-task as a template which is copied to the selected users.

• Any sub-task can be used as a template.
  To create an exemplary template-task use "Create Template Sub-Task" in the "More" menu (more).
•  Adjust your template to your needs. 
   You can use placeholders in the template to access properties of the assigned users (more).
• When your template is ready, use "Copy Subtask to Group" in the "More" menu.
  Add the users or groups you need and proceed (more).