If you consider nuclear family as an entity, it’s e2ee. Practically.
Putting aside the fact that yes, the server can be compromised if somebody chose to attach to the live RAM and recover keys. But practically, nobody will. Same way Google will not deliver a special compromised image of the mobile app on my phone, even though they completely can.
This setup simply does fit the definition. And trying to say it is "e2ee practically" is a bit dishonest: there is no definition for "practical e2ee".
The point of e2ee is that you do not have to trust the server (see Bitwarden for instance).
So what is different in saying „All family devices should see images taken by any device“? They are all clients, including the storage&processing device.
Insisting that E2EE have „ends“ on clients is not useful. It’s much better to define „end“ based on control.
Here’s Wikipedia’s definition:
„End-to-end encryption (E2EE) is a method of implementing a secure communication system where only the sender and intended recipient can read the messages“
Note the complete lack of client/server distinction. It’s simply about intended recipients.
E2ee is quite well established imho. The server at Hetzner (a.k.a. "someone else's computer") is NOT to be trusted in e2ee schemes. Until today I'd be willing to say everyone agrees on this, but now I doubt that :)
Let's see e.g. Wikipedia:
> End-to-end encryption (E2EE) is a method of implementing a secure communication system where only the sender and intended recipient can read the messages
It is only about the sender and intended recipient. In this case, if they actually would self-host, the server and sending devices are in the same entity group and it is encrypted where it matters. In the case of Hetzner, it is not, because Hetzner can access the machines as they are not in the sender's or receivers basement.
But there are some other benefits with E2EE if going strictly with "client-to-client" model - if server is compromised by the bug, there is higher chance that then data gets stolen as plaintext.
The disks are fully encrypted, so the attacker must be careful not to accidentally interrupt power or force a reboot.
And they can’t just log into the machine, it is still a normal Linux machine with passwords.
So they need to attach to a running system and actively hack it, which is completely possible but is not going to be done by a random employee for no reason.