As of this time, it is not possible to create notification rules for task reminders, reminding teammates of an upcoming task.
You can only create notification rules to notify teammates when a task is created, updated or cancelled.
We can send to your teammates a daily task summary of their tasks (only one email per day with full visibility).
A technologically robust solution to emails or SMS tasks reminders would be to have your teammates add the iCal feed to their calendar app on top of notifications. Your teammates will always be able to see the last updated tasks with all relevant details (depending on their task type).
You can also create notification rules to remind them of reservations' check-in and check-out (this is not recommended if you are using tasks and task rules).