Yes you can.
In this golden layout, and in construct you cannot have multiple html windows that you can freely undock. They are inside main window and you cannot move them outside of this main window. So its only one html window but you see boxes inside this main window, and this is easly done in construct 3.
You can create your app and open new page or app in it. We call it "browser bombing", or "pop-up loop attack", and we dont like it. So better dont do this. Just use one window.
If you run multiple constract app on single pc, they can comunicate with each other. You can use multiplayer plugin, you can use remonte database, on local files to do this.