How to make lobby system work without dedicated servers?

I want to make lobby system, where friends can join to one friend, then they looking for session( that is hosted with advanced steam session by another player) and then they all join to one session. The problem is that i can’t use find session because players already in one(lobby). I wonder is there a some way, that i can either find sessions, while players alredy in other or save some sort of variable of players that in one team(like UNetId) and then use this variable to connect them to one session from host?

Greetings @Ozymand1as_I!

In order to setup a lobby system without a dedicated server, please follow these guides on how to implement it, either Peer-to-Peer, or via Steam:

https://dev.epicgames.com/docs/game-services/lobbies-and-sessions/lobbies-and-sessions-introduction

Is there no opportunity to do it with Steam Online Subsystem rather than EOS?

Of course, please check these guidelines, implementing multiplayer with the subsystem, instead of EOS: