Oh jeez...guess his knocked up harem has made Tails come out of retirement. He's gone to Arendelle and kidnapped Elsa and Anna! Why aren't Elsa's powers working?
Simple, magic.
In all seriousness, Tails just got the drop on them real good and managed to make a elixir that negates Elsa's power. Now the the busty princesses are at his 'tender' mercies.