"When you Save in PS Elements the original image is not changed, just the preview of it that is shown in the origanizer"
Elements works like Photoshop, which means changes to the files in the Elements editor are indeed written to the files on your drive or in an edited copy (a version set), and the thumbnails are updated.
If you are working on raw files in the ACR plugin, yes, the raw file is not changed, but its sidecar xmp file is updated when you click on the 'Done' button. It's not so common in Elements because most of the time PSE users use the 'Open' button to further edit in the pixel editor and save a version set in jpeg, psd, tiff...
I am not a Mac user, but Mac experts will tell you that you can't make the organizer and Photos work together. If I remember well the trick is to save a file to your drive from the organizer or the editor, then let Photos 'import' the photo into its secret garden. Also, I have read that there are plugins in Photos to use PSE as an external editor. Please Mac experts, correct me if I am wrong.