Making an Oracle XE instance network wide available
You should only install server software (i.e. Oracle 18c XE) on the server. You should install client software (i.e. Instant Client or full OCI Client) everywhere else. While the server software includes the client, it is intended for local access, or to allow servers to talk to each other. There is no need to (indeed every reason not to) install the full XE server on every client host.
For your server network configuration files, the defaults associated with an XE setup should be fine. The only thing you'd need to double check is that you don't have a firewall blocking access to the server port (1521 by default) for remote clients.