Which version of Jupyterhub and Jupyterlab are you using?
For the latest lab, the way to user RTC is to install the plugin jupyter-collaboration.
Then with your config, user1 should be able to share his server by clicking on the share link (upper right corner) with user2 (logged in).
I recommend to first test your config with a docker before using any cloud provider. See, for example, my recent post.