I’m currently backing up family photos to a black boxes.

Principal is that the photos always in 2 places. My android phone is backed up to dropbox. The wife’s iphone to iCloud also.

Common thinking in IT is that if the data is not stored in 3 places it does not exist.

Relying on a cloud provider is potentially dangerous as you have no control over what they do with your pictures. They may accidentally wipe them, go out of business (unlikely it may seem but someone like Apple may just turn round and go ‘we ain’t providing this service no more’).

Back your phones up to a computer and back the computer up to an external hard drive or NAS box.

Have them on the cloud also but as a fallback position should your computer and external backup solution fail.

Why not just burn DVD’s?

Backup in the same location isn’t that good for fire. Also DVD’s are fragile and have a limited life span.

As above 3 places is good, Dropbox/Google Drive is good as it leaves a copy on your machine.
I use dropbox to mirror a copy on my desktop/laptop and have a copy “Out there”

Flickr gives you 1Tb free space and stores photos in original high res format.

However, after their recent upgrade, the UI is terrible and it’s really, really slow to use, so next to useless for browsing your photos. However, it still works as a backup.

I use 2 hard drives and my PC at work as well as my laptop. Nothing is actually baked up if its not in two physically separate locations.

Just get them on screen, then take a photo of them.