Hi @Kray_zee. Time ago, I used nginx (with rtmp module) for stream to multiple services at once (now I am testing with SRS, that seems to be more powerfull). With that, you can set up multiple pushes to any remote server for each stream push to your local server.
But, like Facebook no longer allows RTMP, but RTMPS, isn’t possible to stream to Facebook using nginx. There are some extra steps to doing something for enabling secure protocols or something (never looked into that. Waste of time for me).
When I actually stream both on Youtube (or any other RTMP service) and Facebook, I set up an stream output in main OBS PC to one service, and another OBS PC for streaming to another service, using NDI source taking Main OBS program video and audio.
Instead of using two ATEM, just sending a/v with NDI throug LAN.
You can also look for another software with multistreaming capabilities (Wirecast, VMix… (maybe ffmpeg too?)) or an online service like Restream (https://restream.io/).