Hi ,
The HTML5LaunchHelper.exe was intended for testing on your own machine and creates a local host that can only be accessed by the machine launching the helper.
If you want to test networking with other computers you will have to create the network functionality either in code or blueprint and run the project. Here is a link for Online Session Nodes.
https://docs.unrealengine.com/latest/INT/Engine/Blueprints/UserGuide/OnlineNodes/
,