ARE WE GUARANTEED TO WIN THEM ALL?
There is no guarantee that we will win all of the three grand prizes, or even the first two even if finishing all quests. It does indeed involve an element of luck, and extra keys will be required to be won from several tries at opening the chests in order to get enough Ice Crowns.
In previous events, it used to be only somewhat likely to win the 2nd grand prize, and highly unlikely to win the third grand prize, without investing in additional event currency.
This is obvious when we look at the total Ice Crowns required, and how many keys it would take to obtain as many (without any tries resulting in additional keys) -
Yet adding up all the keys available from quests, we can see that we would need nearly half our tries resulting in extra keys, which is not statistically impossible, but also not likely.
With the addition of Double Days, however, it is now possible and even likely for players who complete all or even most quests to win all 3 Grand Prizes.