Let's start by making sure we are on the same page with regards to the role of clients and servers:
One (and only one) of your machines is running the node js server. We'll call the the first machine.
Browsers running on the first machine are able to reach the server and get the pages it servers, establish websocket connections to the server, etc.
The other machine (which we'll call the second machine) is not running a node js server and but it is running a browser which is pointed at the server on the first machine.
On the second machine, does the demos/index.html page get displayed (has the list of demos on it)?
If not, you may have general network problem. Try running both machines on the same subnet, physically plugged in to the router (not using wifi). If that solves your problems, you simply need to run your server some place where it can found by both machines.
If so, then you've got websocket problems. Those are rare, but could be caused by a firewall on the first machine. Try turning off the firewall.
Beyond that you'll need to supply a more detailed description of your network environment, what demo in particular you are trying to run, and what browser (brand/version) you are using. We're good, but we're not mind readers :-).