If you don't have an iPhoto library on your secondary Mac, create a new library in Photos and turn on iCloud Photo Library. If you have duplicates of the same photo on each computer, iCloud should automatically resolve those conflicts when it syncs, providing you with just one version of your photos when the sync process finishes. If you have an iPhoto library on that secondary Mac, follow the same steps as above - import your library, then turn on iCloud Photo Library. Now, open your other Mac, and launch Photos.

You can check off Optimize Mac Storage to save space on your Mac by only saving a percentage of images and video locally - the rest will be thumbnails that you can click on to download when you want to.You can also check off the box for Download Originals to this Mac if you have the space.Select Preferences (or do this quicker by pressing ⌘,).

You can do this by following these steps: Once you've imported your biggest library on your Mac, make sure iCloud Photo Library is turned on and syncing. VPN Deals: Lifetime license for $16, monthly plans at $1 & more