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Definitely not one person as they are often playing freestyle and one is in Italy and the other in the US.
As for secret alliance, in your game the winner took the other out first. The other games do not appear to show any teamwork. There are a couple of games in 3 player where they are the last 2 to join, but both games have each other attacking each other a lot. Given their feedback so far, this looks like it's highly unlikely.