Raid/NAS, as many others have said, isn't a backup.

However, you could have a single NAS and backup to AWS Glacier where storage costs for larger files is cheap going in and getting out in DR scenario is expensive, but maybe covered by your insurance depending on the DR event.

Given it's for your death, why not have multiple copies in multiple formats? For for Mac, one in ext4 and one in NTFS? Youd have multiple copies of your will so why not this.

I've used 7digital and hdtracks.

Word of caution on 7digital; I've found that sometimes they'll lose the licence for the files so my downloads will no longer be accessible. Always download immediately and backup.

Also found one file on a NIN album corrupt.