Secure, accessible geo backup

[Nombus]

Hey, wizards,

I'm looking to complete my backup solution with a geographic backup. My goal is two-fold:

1. If my house goes up in flames or my NAS A (DS920+ with 4x16TB) gets hacked by a super wizard, all my files are still safe off-site on destination B.
2. My friend, who will host the destnation B, can edit the files directly on the remote location (to avoid latency and downtime issues) and those files will get updated to the primary NAS.

My budget does not permit a subscription cloud service. I first thought of making destination B a DS1520+ (5-bay) with 4x14TB + 1x6TB drives (it's significantly less expensive than another NAS A, yet has the same usable storage after SHR as NAS A, according to RAID Calculator | Synology Incorporated), using Drive ShareSync, Hyperbackup (HB), or Snapshot Replication (SR). I'm assuming ShareSync, HB, and SR don't need NAS B to be the same drive structure as NAS A. But even if I made NAS B identical to NAS A, I run into concerns with each:

1. ShareSync fails goal 1? If the source NAS gets hacked, couldn't they delete the NAS A contents and remove Drive version history to delete everything on NAS B?
   1. Potential con: if one NAS were to spaz out in a fire and tell the other NAS with its dying breaths to delete everything, I wonder if you could recall all the files en masse with version history (instead of one at a time).
   2. SR Shared Folder appears to fail goal 1, but I don't know SR that well.
2. HB fails goals 1 and 2? Couldn't a NAS A hacker delete all the backup versions stored on NAS B? Also, there's no way to edit the files on NAS B--particularly not in a way that will sync with NAS A.
   1. SR One-to-many and Extended Replication also appear to fail goals 1 and 2 for the same reasons.

Am I stupid and just don't understand backup theory? Are my goals dumb? Do I misunderstand ShareSync, HB, or SR? Is there a solution inside Synology, or perhaps even a less expensive solution outside of the Synology eco-system?

Thanks, y'all.