Question: which younger daughter of Richard Nixon was Tricia Nixon Cox also a sister too 

Context articles: Richard Nixon Foundation
John H. Taylor (bishop)
Christopher Nixon Cox
Nixon v. General Services Administration
Melba Tolliver
Tricia Nixon Cox
Courteney Cox
Julie Nixon Eisenhower
Jenn Gotzon
Zilch memo

The Richard Nixon Foundation is a not-for-profit organization based at the Richard Nixon Presidential Library and Museum in Yorba Linda, California.
 It was founded in August, 1983 by Richard Nixon, 37th President of the United States, and served as the governing body of the Nixon Library for nearly twenty years.
 Today it operates the Nixon Library in conjunction with the National Archives and Records Administration, which is an entity of the federal government of the United States, in addition to undertaking charitable and education-based activities.
John Harvey Taylor is bishop coadjutor of the Episcopal Diocese of Los Angeles, and the former post-Chief of Staff to Richard Nixon, and served as the Executive Director of the Richard Nixon Library & Birthplace Foundation.
 Taylor had served as director of the privately owned and funded Richard Nixon Library and Birthplace prior to it joining the federal presidential libraries system, and becoming the Richard Nixon Presidential Library.
 Taylor is also an Episcopal priest, and currently serves as the Vicar of St. John's Episcopal Church and School, located in Rancho Santa Margarita, Orange County, California.
 In December 2016, he was elected to serve as Bishop Coadjutor of the Episcopal Diocese of Los Angeles.
Christopher Nixon Cox (born March 14, 1979) is an American lawyer based in New York.
 He is the son of Tricia Nixon Cox and Edward F. Cox and grandson of Richard Nixon, the 37th President of the United States and Pat Nixon, First Lady of the United States.
Nixon v. General Services Administration, 433 U.S 425 (1977), is a landmark court case concerning the principle of presidential privilege and whether the public is allowed to view a President’s “confidential documents”.
 The Presidential Recordings and Materials Preservation Act, signed into law by President Gerald Ford in 1974, ordered that the Administrator of General Services obtain President Richard Nixon’s presidential papers and tape recordings.
 In addition, the Act further ordered that government archivists seize these materials.
 These archivists would preserve the material deemed historic and return to former President Nixon the materials deemed as private.
 Furthermore, this Act stated that material that was preserved could be used in judicial hearings and proceedings.
 Immediately after this Act was enacted, Richard Nixon filed a lawsuit in a federal district court claiming that the Act violated the principle of separation of powers, the principle of presidential privilege, Nixon’s personal privacy, his First Amendment right of association, and further asserted that it amounted to a constitutionally prohibited Bill of Attainder.
Melba Tolliver (born 1939) is an American journalist and former New York City news anchor and reporter.
 She is best remembered for her defiant stance against ABC owned WABC-TV when she refused to don a wig or scarf to cover up her Afro in order to cover the White House wedding of President Richard Nixon's daughter Tricia Nixon in 1971.
Patricia "Tricia" Nixon Cox (born February 21, 1946) is the elder daughter of the 37th U.S. President Richard M. Nixon and First Lady Pat Nixon, and sister to Julie Nixon Eisenhower.
Courteney Bass Cox (born June 15, 1964) is an American actress, producer, and director.
 She is best known for her roles as Monica Geller on the NBC sitcom "Friends", Gale Weathers in the horror series "Scream", and Jules Cobb in the ABC/TBS sitcom "Cougar Town", for which she earned her first Golden Globe nomination.
 Cox also starred in the FX series "Dirt".
 She owns a production company, called Coquette Productions, which was created by Cox and her then-husband David Arquette.
 Cox also worked as a director on her sitcom "Cougar Town" and the television film "Talhotblond".
Julie Nixon Eisenhower (born July 5, 1948) is the younger daughter of Richard Nixon, 37th President of the United States, and Pat Nixon, First Lady of the United States.
Jenn Gotzon (born May 18, 1979) is an American film actress, international model, motivational speaker & author who had her career break portraying U.S. President Richard Nixon's daughter Tricia Nixon in Ron Howard's 2009 Academy Award-Nominated film "Frost/Nixon" opposite Frank Langella.
 Since 2010, Gotzon starred in many uplifting and redemptive feature films, including, mystery-drama "Doonby" opposite John Schneider, Robert Davi, Ernie Hudson, 2014 Oscar Nominated (rescinded) inspirational French and Indian War true-story "Alone yet Not Alone", comedy-drama "God's Country" opposite Daniel Hugh Kelly, NSA cyber war-thriller "Dragon Day", inspirational drama "I Am Gabriel" (Dean Cain, Gavin Casalegno (Young Shem in Noah), first silent evangelical feature film "The Good Book", "Dante's Hell Documented" portraying heroine Beatrice alongside Dante portrayed by Eric Roberts, inspirational rom-com "Princess Cut", hysterical sitcom TV pilots "Shelter" (Alicia Minshew) and "Heaven Help Us" (Nancy Stafford, Lee Meriweather), 2014 award-winning music video by Lamon Records "Walls" by artist Sean Guerrero.
A memorandum known as the Zilch memo was an American government document sent by National Security Advisor Henry Kissinger to President Richard Nixon on January 3, 1972, about the military situation in Laos during the Vietnam War.
 On the memo, in his own handwriting, Nixon described the decade-long bombing campaign by the United States in Southeast Asia as a "failure," having achieved "zilch," despite public comments to the contrary.
 Just the day before, January 2, Nixon told CBS News reporter Dan Rather in an interview that the bombing was "very, very effective."
 Previously missing from the Richard Nixon Library, the memo was discovered in the possession of Alexander Butterfield, who served as the Deputy Assistant to President Nixon from 1969 to 1973, by "Washington Post" reporter Bob Woodward, who subsequently published it in his 2015 book "The Last of the President's Men".