In this task, you're given passages that contain mentions of names of people, places, or things. Some of these mentions refer to the same person, place, or thing. Your job is to write questions that evaluate one's understanding of such references. Good questions are expected to link pronouns (she, her, him, his, their, etc.) or other mentions to people, places, or things to which they may refer. Do not ask questions that can be answered correctly without understanding the paragraph or having multiple answers. Avoid questions that do not link phrases referring to the same entity. For each of your questions, the answer should be one or more phrases in the paragraph, and it should be unambiguous.

Passage: After Minh had ordered the rebels to search the areas known to have been frequented by the Ngo family, Colonel Phạm Ngọc Thảo was informed by a captured Presidential Guard officer that the brothers had escaped through the tunnels to a refuge in Cholon. Thảo was told by Khiêm, his superior, to locate Diệm and prevent him from being killed. When Thảo arrived at Ma Tuyen's house, he phoned his superiors. Diệm and Nhu overheard him and Thơ drove them to the nearby Catholic church of St. Francis Xavier, which they had frequented over the years. Lieutenant Thơ died a few months later in a plane crash, but his diary was not found until 1970. Thơ recorded Diệm's words as they left the house of Ma Tuyen as being "I don't know whether I will live or die and I don't care, but tell Nguyễn Khánh that I have great affection for him and he should avenge me". Soon after the early morning mass was celebrated for All Souls' Day (the Catholic day of the dead) and after the congregation had left the building, the Ngô brothers walked through the shady courtyard and into the church wearing dark grey suits. It was speculated that they were recognised by an informant as they walked through the yard. Inside the church, the brothers prayed and received Communion.A few minutes later, just after 10:00, an armoured personnel carrier and two jeeps entered the narrow alcove housing the church building. Lieutenant Thơ, who had earlier urged Diệm to surrender, saying that he was sure that his uncle Đỗ Mậu, along with Đính and Khiêm, would guarantee their safety, wrote in his diary later "I consider myself responsible for having led them to their death".
What are the first names of the two brothers who escaped through the tunnels to a refuge in Cholon?