Task: Question Answering
Input (English): Passage: Mark Bradley is a radio commentator whose pilot, Joe Walker, is flying him across the South Pacific to a conference in Australia. 
Engine trouble develops, and Walker must make a forced landing on the beach of a small, uncharted island inhabited by Dr. Paul Lujan. On the island with Lujan are his three naive daughters, who have never known another man except their father. 
Lujan, unfriendly to the point of hostility, orders the intruders to leave his island, but one of their aircraft's two engines is too badly damaged for them to be able to comply without first making repairs. He grants them a couple days in order to do so. In the meantime he grudgingly introduces Bradley and Walker to his trio of young, beautiful daughters, Venus, Urana, and Mercuria. The two men soon learn that Dr. Lujan was an atomic scientist who fled the civilized world with his family because he fears the havoc being caused by the discovery of nuclear energy.
To the doctor's disapproval, his two older daughters easily fall in love with the two attractive strangers and try to help them, while the third, 16 and jealous of her sisters, tries to foil their plans. This forces them to make a choice between staying on the island with their father or returning with the two men to a civilization they have only experienced via short wave radio broadcasts. When Bradley mentions that he plans on doing a radio broadcast about Lujan and his island location after he returns to civilization, the Dr. begins to scheme a way to keep the men and his daughters on the island. 
Question: What are the full names of the characters with whom 2 of Dr. Lujan's daughters fall in love?
Output (English): Joe Walker.