You cannot directly select attacks for the Magus Sisters, but instead from a few options.
The Sisters are more likely to perform unique attacks when you select "Do what you will" or "Go! Go!" from the menu. These unique attacks are: Camisade (shoots blades of fire), Razzia (launches Sandy onto an enemy), and Passado (fire a burst of stingers at the enemies).
When Cindy, Sandy and Mindy are all in overdrive, you will be able to select "Combine Powers!". This will cause the sisters to combine powers and launch a hugely destructive attack.
