This is a great question. In many ways Kino and Juana are the same. They are both basically simple people. They are content with life. They are committed to their traditions and cultural values, and they have good work ethics. For instance, Juana is a submissive and supportive wife and Kino is a hard working husband and father.
What change all of this and bring out the differences in their character is the scorpion bite of Coyotito and the discovery of the great pearl.
What makes them different is that Kino is only able to see the positive element of the pearl, where as Juana is able to see that the pearl for all its beauty is also destructive. For example, it never crosses Kino's mind that the pearl can bring more problems. It never occurs to him to throw the pearl away. Here is a quote of how Kino view the pearl:
"In the pearl he saw Coyotito sitting at a little desk in a school, just as Kino had once seen it through an open door. And Coyotito was dressed in a jacket, and he had on a white collar and a broad silken tie. Moreover, Coyotito was writing on a big piece of paper. Kino looked at his neighbors fiercely. 'My son will go to school,' he said, and the neighbors were hushed. . . ."
As the novella progresses, Juana is different as she is able to see problems in the pearl. She at one point wants to throw it away, but Kino does not allow her. He even hits Juana, at his low point, to get the pearl back.