WebRTC with 3 users connection
Solution 1:
A mesh of 3 users means each user sets up two connections, one to each of the other two users. At each client's end, these are two entirely different RTCPeerConnections, and you can't reuse candidates between them, as each candidate contains port numbers allocated specifically for the media and the target it is to be sent to.
If you know how to set up one connection, you know how to set up two. Just keep things separate.