You divide the damage as you put Gang of Devils’s triggered ability on the stack, not as it resolves. Each target must be assigned at least 1 damage. (In other words, as you put the ability on the stack, you choose whether to have it deal 3 damage to a single target, 2 damage to one target and 1 damage to another target, or 1 damage to each of three targets.)
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.