Read (only) access should be fine. What makes it complicated is if there can be writes from multiple locations. Basically, the simple version would be to just periodically copy the data from the primary to all secondary locations.

I can see why you’d want to go with an off-the-shelf NAS. But, I would carefully check if it supports your use case, as it’s quite advanced.

If the data only needs to be read & written from a single server (and the others are just backups), you can also use simpler replication instead of synchthing. E.g. syncoid or TrueNAS replication. It sounds like you should be able to do that with separate datasets per household in your usecase.

I would probably go with a simple approach like this:

• ZFS: Each house gets a “NAS” that provides a ZFS filesystem to store the data. This gives you the ability to share the drives across your use cases (you, rest of the family), snapshots, RAIDZ support, and usage quotas. For the OS, you could use what you prefer (TrueNAS, Debian, Ubuntu, …).
• Syncthing to synchronize the files across the servers/houses. This allows you to read and write data from anywhere and syncthing will mirror the writes to the other places. I use it to synchronize data across 5 devices and it works quite well.

There are probably more advanced (enterprise?) ways to handle the file synchronization. But, I think this hould be good enough for normal, personal use. The main disadvantage is that you’re only synchronizing the current data (excluding the ZFS snapshots). On the other hand, this also allows you to mix file systems if necessary.