OpenVidu session topology is not designed to have one participant publishing to all sessions at the same time. You you have to find some way to achieve this in the most efficient way.
There are several possibilities:
Several independent sessions: It is easy to implement, but the “big publisher” should join and publish in every session. Too much upload bandwidth.
Create a big session with all participants: And the you can “virtually” divide some participants into virtual sessions. But you can not reuse any sample code because it assumes all participants in the same session belongs to that session. Also, all participants will receive all the notifications from all other participants from other virtual sessions. Maybe too much notification overload.
Several independent sessions with “virtual multiplexed publisher”: You can create multiple sessions with 4/6 participants on it. Also, you can create a session with the broadcaster-publisher participant. And then, connect in the server side the broadcaster session with the rest of the sessions. How to connect two sessions in OpenVidu? The feature is not available in the API, you should cheat OpenVidu to do it. The idea is to simulate a participant in a real browser but executed in the server. So this fake participant can subscribe to the broadcaster in their sessions and simulate another fake participant as a publisher in the rest of the sessions. How? One strategy is executing openvidu-browser SDK in Node.js and using Kurento as a WebRTC stack. In that way, you can later manipulate Kurento MediaPipeline as you wish to get media from broadcaster and send it to the rest of the sessions. It is not easy, but you can get inspired from the browser-emulator we have implemented to load test OpenVidu. As the name suggest, it is a browser-emulator that executes openvidu-browser SDK in a Node process using Kurento under the hood: openvidu-loadtest/browser-emulator at master · OpenVidu/openvidu-loadtest · GitHub
You can use OpenVidu PRO or OpenVidu Enterprise. Both versions will work, but with OpenVidu Enterprise you will have more users per CPU. Also, take into account that OpenVidu Enterprise is still in beta, so some things can go wrong.