On Mac:

Make sure that your team members are added as followers to the task, after that click on the task -> go to reminders section – > set the time of the reminder -> tick “Remind all followers”:

Screenshot 2016-01-27 10.42.50

On Windows:

Make sure that your team members are added as followers to the task, after that click on the task and go to the Conversation box on your right hand side -> type in the command using the following format “Remind all followers {next Monday at 11 am}”: