I just set this up earlier today, WFO.

PG is correct. Use the host machine IP in the remote_hosts.cfg file on the local machines.
The IP you cited from the instructions is just an example.
I was a bit confused by the language there myself.

As TRN said, you MUST restart BOINC manager on the local machines after creating and editing the remote_host.cfg file. (I didn't have to reboot the machines-just exited and restarted BOINC.)
In my case, relaunching BOINC manager on the local machines immediately gives a firewall prompt which I accepted.
After that, the Boinc Tasks search function on the host machine picked up the locals and all I had to do was provide the password from the gui_rpc_auth.cfg file on the local machines.

If you're running a different OS (I'm on W7ProX64) you may have to handle the firewall thing manually, IDK.

I handled the whole thing via RDC from the host machine.

Keep asking, we'll get it.