deleting pictures without deleting on other devices

You have two options: 1) disconnect your Photos application from iCloud and 2) use the optimize option of Photos iCloud.

1. If you open System Preferences, choose the iCloud tab and click on the Photos checkmark to deselect it you’ll disconnect your computer’s Photos application from iCloud but be given the option to keep your pictures on the computer or delete them. If you make this choice you can delete pictures from the computer without deleting them from iCloud. Any new pictures you take will have to be manually moved onto the computer.
2. In the iCloud tab of System Preferences you may click the Options button and select the optimized photos option. This keeps the original full size photos in the cloud but puts much smaller versions on your computer (which take up less space). The advantage of this option is you may be able to keep all your photos because the space saving is significant. This disadvantage is that if you want to edit any pictures on your computer you need to be connected to the Internet so you can download the original to edit it. (When you finish the edit your computer will once again have only the optiimized version.)