How do guests find out that their photos are ready? Do I have to message everyone myself?

That's the whole point of the notification system — you don't. Snaptide sends automatic notifications via WhatsApp and email when you publish an album, when a guest's images are ready, or when access is granted. So the workflow is: upload, publish, and the platform tells everyone who registered that their photos are waiting. It's the difference between a photographer spending an evening copy-pasting messages and a photographer who hits publish and moves on to the next edit.