You might be interested in looking at this RTC example for ideas about how to make bi-directional data flows for arbitrary groups of participants (or players) work through a relay.

https://hang.live/

It uses a feature we haven't yet implemented, but we're thinking about how we might implement it at our scale, SUBSCRIBE_ANNOUNCES[1].

[1]: https://www.ietf.org/archive/id/draft-ietf-moq-transport-12....