Can guests delete photos from the gallery?

Yes, guests can only delete photos/videos that they have uploaded. 

Once you are in the gallery, select any of your own photos that you wish to delete. In the bottom-right corner, you'll see a trash can icon. Select trash-can and click “Yes, Delete”. This will remove the photo from the gallery permanently.

Guests do not have the ability to delete content uploaded by others - only the host has the ability to remove any and all content if desired.