The amount of bonus numbers (one to five), which numbers they actually are, and their associated multipliers are all determined by a random number generator. This is part of safe and fair gaming, having thoroughly tested RNGs so that all elements of any casino game are random, i.e. a gamble.
As such, no one decides on the lucky numbers or multipliers. Which ones appear are a matter of luck. Or more specifically, a matter of good luck if you’ve bet on one and the number goes on to win.