I would strongly recommend signing up for either Backblaze, or using something like iCloud Photos or Google Photos.

My entire 100,000 photos, 20 year library is now in iCloud photos. It's constantly synced and backed up to icloud. Then I have it pulled down in full to a mac that then backs up to backblaze.

Lots of ways to do it, but thats one. :)

For $5-10/month you can get unlimited backup from a machine with Backblaze including your external drives.