Use the phrase in their right minds to describe people who are calm, reasonable, and sane. People in their right minds would never climb into the lion enclosure at the zoo.
When people are in their right minds, they make reasoned decisions and act in a normal, understandable way. It's far more common to describe someone, however, as not in his right mind: "Your brother was not in his right mind when he drove the car into that snowbank." You may suspect that you yourself are not in your right mind if you come home from the animal shelter with seven cats.