Photos don't delete from hard drive

Just to be sure - after you deleted the photos and videos, did you empty the "Recently Deleted" album? Otherwise the deleted photos will stay for another month, until they will finally be deleted. Reveal the "recently Deleted" album from the "View" menu.

I have Photos and Aperture, I just deleted iPhoto

Is your current Photos library an iPhoto Library or an Aperture library, that you migrated to Photos? Then deleting photos from Photos will not release the disk space, until you delete the corresponding mage file from the original iPhoto Library or the aperture library as well. The original Aperture/iPhoto library and the Photos library are sharing the image files by hard links. Only when both the original image and the hard linked image have been deleted, will the storage be released. See: Photos saves disk space by sharing images with your iPhoto or Aperture libraries - Apple Support

A possibly related problem: I'm seeing a lot of empty albums under 'iphoto events', like this:

The iPhoto Events folder is holding an album for each each Aperture project or iPhoto event you migrated. Since you deleted photos, it would be only natural, if some of these albums are now empty.

I guess I assumed the empty events would disappear, they're auto-created date 'events', if that's the same as an album I can understand why it's still there.

Photos does not have events, only moments. So your events have been faked and recreated al albums, when you library has been converted to a Photos library. This document describes, how Photos is handling contents from Aperture and iPhoto, that cannot be recreated in Photos:

How Photos handles content and metadata from iPhoto and Aperture - Apple Support

I swear I checked the deleted items folder yesterday and found it empty.

Perhaps you used the delete key ⌫ and not ⌘⌫ (command-delete) to delete the photos from the albums. This will just have removed the photos from the albums and not deleted them. The delete-key alone will only delete the photos when used in a moment. ⌘⌫ will delete the photos wherever you use it.