These notifications are only available for your tasks. If your following tasks assigned to your colleagues, you will receive notifications when these get actioned, but here is another way to keep track of their tasks: you can create a report for all tasks assigned to them in the next 24h. If you save this report, it will automatically appear in your sidebar and update every day (I’ve added below a screenshot of the criteria you should use for this); you can also rename this report (all steps are available in this article). You’ve two options to organise these reports: you can either create one for each member of your team and sort it by assignee to easily identify who works on what; alternatively you can create one per person. Again, this won’t trigger notifications, but they’re very easy to access and should help you to keep an eye on your team workload!
Hope this helps! Have a great day