The number of players choosing the highest number doesn't change how much damage is dealt. For example, if the four players in your game reveal 4, 7, 7, and 7, Wheel of Misfortune will deal 7 damage to each of the last three players and those three players will discard their hand and draw seven cards.

For each player to secretly choose a number, that player should write down their chosen number without showing it to anyone else. Each player then keeps their number secret until all players simultaneously reveal their numbers.