Also, in some minigames like Manor of Escape and What Goes Up..., when all 4 players finish at the exact same time (such as when they're all being controlled by one person), the finishing whistle is much louder (I assume it's played 4 times, once for each player finishing), and every player gets 40 coins (and I would assume 80 if it's a lucky minigame).
I assume what's going on is that there's like a flag set when the minigame ends to award the winner(s) 10 coins, and, since I assume all 4 players are ending it separately, it sets 4 of these flags and awards all of the winners 10 coins 4 times each for 40 coins.
Side note, I don't think random lucky minigames can have a 3x multiplier, or, at least, I haven't seen it when I've played (but I do think I've seen it in videos of earlier versions).