Complex sentence: Sinnoh League Champion Cynthia housing them as they all prepare the Pokémon World Tournament Junior Cup, hosted by Unova League Champion Alder; training for the upcoming Unova Pokémon League conference; and meeting the legendary Pokémon Meloetta.
Split into simpler sentences: Sinnoh League Champion Cynthia houses them as they all prepare for the Pokémon World Tournament Junior Cup, which is hosted by Unova League Champion Alder. They train for the upcoming Unova Pokémon League conference and meet the legendary Pokémon Meloetta.