Nick Sidi
Nick Sidi( born 22 February 1966 in Manchester, England) is an English actor.
He is the son -in- law of actress Rosalind Knight and brother- in- law of actress Susannah Elliott- Knight.
He often plays drama or comedy roles on television and frequently appears in BBC dramas.
Robert Vadra
Robert Vadra is an Indian businessman, entrepreneur and the husband of Priyanka Gandhi.
He is the son -in- law of Sonia Gandhi and Rajiv Gandhi, and the brother- in- law of Rahul Gandhi.
Romanos Argyros (10th century)
Romanos Argyros was a Byzantine aristocrat and son-in- law of Emperor Romanos I Lekapenos.
Wyndham Goold
Wyndham Goold( 1812-1854) was a Member of Parliament( MP) for County Limerick from 1850 to 1854.
Goold was educated at Westminster School and Trinity College, Dublin.
He was the son in law of Frederick Falkiner Goold, Archdeacon of Raphoe and brother in law of Bishop Hamilton Verschoyle
William Rose Benét
William Rose Benét (February 2, 1886 – May 4, 1950) was an American poet, writer, and editor.
He was the older brother of Stephen Vincent Benét.
Greg Penner
Gregory B. Penner( born December 18, 1969) is an American businessman and venture capitalist.
Penner was named the chairman of Walmart on June 5, 2015.
He is the son-in- law of S. Robson Walton and the grandson- in- law of Sam Walton, the founder of Walmart.
Robert W. Levering
Robert Woodrow Levering( October 3, 1914 – August 11, 1989) was a U.S. Representative from Ohio, son-in- law of Usher L. Burdick and brother- in- law of Quentin N. Burdick.
Marjorie Flack
Marjorie Flack (22 October 1897 - August 29, 1958) was an American artist and writer of children's picture books.
Flack was born in Greenport, Long Island, New York in 1897.
She was best known for "The Story about Ping" (1933), illustrated by Kurt Wiese, popularized by Captain Kangaroo, and for her stories of an insatiably curious Scottish terrier named Angus, who was actually her dog.
Her first marriage was to artist Karl Larsson; she later married poet William Rose Benét.
Her book "Angus Lost" was featured prominently in the movie "Ask the Dust" (2006), starring Colin Farrell and Salma Hayek, in which Farrell's character teaches Hayek's character, a Mexican, to read English using Flack's book.
Marjorie Flack's grandson, Tim Barnum, and his wife, Darlene Enix-Barnum, currently sponsor an annual creative writing award at Anne Arundel Community College.
The award, called The Marjorie Flack Award for Fiction, consists of a $250 prize for the best short story or children's storybook written by a current AACC student.
Charles Francis Norton
Charles Francis Norton( 1807 – 1835) was a 19th- century Member of Parliament for Guildford.
Norton was also a Captain of 52nd Light Infantry; son-in- law of Sir Colin Campbell; brother- in- law of writer Caroline Norton
Lee Chan-hyuk
Lee Chan- hyuk( born September 12, 1996), is a South Korean singer, songwriter and producer.
He debuted as a member of the sibling duo AKMU in April 2014, under YG Entertainment.

Question: Who is Marjorie Flack's sibling-in-law?
Answer: Stephen Vincent Benét