To delete them from iCloud, after doing the above, reopen Photos with the option/alt key held down and create a new system Library. After syncing, you can now delete photos from your computer while maintaining a master copy on the computer. When you have finished deleting and the delete has synced, you can delete the Library.
Then reopen Photos with the option/alt key held down and select your original Library.
The only other way I am aware of is to do a manual delete at iCloud.com/Photos. Hold down the command while selecting the photos. Then click the Trash Can. You can also try selecting a moment, then click the Share button, and then cancelling the Share. The photos should remain selected.