Did you consider something like a Synology NAS, which has free mobile apps for syncing?
the reliability of a backup system is inversely proportional to the number of moving parts
Hence why I use beyond compare to manually sync files to two physical mediums from the master copy on my laptop. One encrypted USB stick I carry on me at all times and one hard disk that lives in a fire safe.
I'm surprised I haven't seen a NAS with the hard drive enclosure fire-rated.