I don't think the rules of the game ever state what would happen if two people play the exact same hand in the exact same suit, which I feel like could end up backfiring on the game runner if the rules weren't rigged properly in their favour. e.g. Even after you've defeat all your opponent's royal flushes since you know where they are, what happens if the opponent plays their straight flush of spades against yours? Unless they win in that situation, I guess it wouldn't matter. Even if they did win they could only at best force a tie if they played conventionally.
Either way it's kind of hilarious how stupidly rigged this game is, to the point where it makes you wonder why Junko actually bothers running the game in the first place. Once she's lured people inside her house she may as well just chain them up and take their teeth.