Shared calendars not appearing on iPad or iPhone.

At work, we all have Apple devices and we sync calendars with Outlook. We share calendars so we can all see what we're doing. I have set up a new iPhone, iPad and Windows laptop for a new employee. I have set up his calendar to share with us and vice versa. Everything is showing when we go into icloud.com on the laptop but they're not showing on the iPad or iPhone. I've checked that everything is switched to ON in the settings.

The calendars are also showing in Outlook on the laptop.

Any ideas?

Thanks

Sue