Photos on multiple computers
Use iCloud Photos. It's really nice having a single shared iCloud Photos Library between your Mac and iOS devices.

Once you're using iCloud Photos, any favorites / edits / deletes that you make on your iPad will be synced to your Mac.


  I don't want to pay for space that I already have at home


You're paying for it, but consider Apple's iCloud as another offsite backup, of which you can never have enough. Consider the cost of the subscription similar to the cost of another backup HDD at home. And it's a better backup for the photos stored on your iOS devices.


  I want to know for sure that all my masters are in my possession


There is a Download Originals to this Mac setting in Photos for the Mac that allows you to keep all original photos on the Mac (as opposed to downloading them on demand from the Cloud / optimizing storage).

Using this setting should keep your current Mac / backup setup roughly the same. Local backups of your computer will continue to back up ALL of your photos.



The originals will still be stored and backed up on your Mac.