As an FYI I love going into networking theory, but my goal is to work on Bubble Server. Bubble Server is written to be C2 friendly, useable for both Client AND Server logic, while providing tools to get Mp game going easily. So giving solutions to other tools are in the end counter productive to my own agenda, but I can offer advice and a direction to achieve. Just not final solutions :D :)
Here is how you should do it. use Clay.io to do everything in the multiplayer setup. Room setup, room names, chatting, room propertiers(number of players, maps...)... so on ect. Once the room is defined. Send the room info to each player. then the players connect to the pubnub room.
I didn't create Clay.io, and I'm not an expert. So anything Clay.io related is definitely better to talk to Austin :) and use the Clay.io thread. Once you get all that done. Then pubnub thread for info :)