Handling Local "Splitscreen" Players in an Online Session

Removing non-primary players from the session

There is not supported server-sided operation to remove a non-primary player ("local splitscreen player") the way UGameplayStatics::RemovePlayer or UGameInstance::RemoveLocalPlayer would. A workaround is to make the client-instance remove the player themselves through a client RPC.

Differenciating between primary players and non-primary players

Non-Primary players ("local splitscreen players") use a UChildConnection rather than the primary player's UNetConnection. From the server, you can cast to the PlayerController's UChildConnection to see if it's a primary player or not.

Cast<UChildConnection>(PC->Player)