I can add overlays okay.

they appear if I click on the calendar title and it opens in its own page but they don't show on the home page.

Sorry, I'm not explaining that very well.

The overlays just don't show up when I'm viewing the calendar on the home page but they do show if I click on the calendar title and just view it by itself without the rest of the home page.

When you add a calendar overlay on any page, you need to go to properties of the webpart and enable all calendar which will have calendar overlay