Putting it all together

Client 1 and Server 1 share the same machine. Similarly, Client 2 and Server 2 share a different machine.

Server-to-server relationships

Server 1 and Server 2 are personal servers. Server 3 and Server 4 are shared servers.

Server 1 pushes changes to and fetches changes from Server 4. So does Server 2. Server 2 can fetch the changes Server 1 pushed, enabling the two personal servers to share content.

Shared servers 3 and 4 fetch and push changes from and to each other.

Client-to-server relationships

From the point of view of Client 1, Server 1 is a local server and Servers 3 and 4 are remote servers.

From the point of view of Client 2, Server 2 is a local server and Server 4 is a remote server.

Client 3 interacts with Server 4 without an intervening personal server.

Server3 and Server4 are relating within a centralized architecture, rather than a distributed architecture.