Both the doctor and the priest try to cheat Kino out of his new found fortune. What are their motivations? Is this ethical behavior?

The priest saw the money as a way to benefit his church, to make repairs that were long overdue.

It came to the priest walking in his garden, and it put a thoughtful look in his eyes and a memory of certain repairs
necessary to the church. He wondered what the pearl would be worth.

The doctor was interested in the money the pearl would gerner for personal reasons, as a way to return home to Paris as a wealthy man.

And the doctor's eyes rolled up a little in their fat hammocks and he thought of Paris. He remembered the room he had lived in there as a great and luxurious place, and he remembered the hard-faced woman who had lived with him as a beautiful and kind girl, although she had been none of these three. The doctor looked past his aged patient and saw himself sitting in a restaurant in Paris and a waiter was just opening a bottle of wine.

Their motivations were self-serving.... they were not ethical. Neither man had the time of day for Kino prior to the discovery of the pearl. They each desired to use Kino in their own way.