Question: Are Sergei Prokofiev and Modest Mussorgsky both Soviet composers?

Context articles: Modest Mussorgsky
Sergei Prokofiev
Semyon Kotko
Piano Sonata No. 9 (Prokofiev)
Piano Concerto No. 2 (Prokofiev)
Violin Sonata No. 2 (Prokofiev)
Lieutenant Kijé (Prokofiev)
Visions fugitives
Sergei O. Prokofieff
Konstantin Saradzhev

Modest Petrovich Mussorgsky (Russian: Моде́ст Петро́вич Му́соргский ; ] ; 21 March [O.S. 9 March] 1839 – 28 March [O.S. 16 March] 1881 ) was a Russian composer, one of the group known as "The Five".
 He was an innovator of Russian music in the romantic period.
 He strove to achieve a uniquely Russian musical identity, often in deliberate defiance of the established conventions of Western music.
Sergei Sergeyevich Prokofiev ( ; Russian: Сергей Сергеевич Прокофьев , "Sergej Sergejevič Prokofjev" ; 27 April 1891 – 5 March 1953) was a Soviet composer, pianist and conductor.
 As the creator of acknowledged masterpieces across numerous musical genres, he is regarded as one of the major composers of the 20th century.
 His works include such widely heard works as the March from "The Love for Three Oranges," the suite "Lieutenant Kijé", the ballet "Romeo and Juliet" – from which "Dance of the Knights" is taken – and "Peter and the Wolf."
 Of the established forms and genres in which he worked, he created – excluding juvenilia – seven completed operas, seven symphonies, eight ballets, five piano concertos, two violin concertos, a cello concerto, a Symphony-Concerto for cello and orchestra, and nine completed piano sonatas.
Semyon Kotko (Russian: Семён Котко ), Op. 81, is an opera in five acts by Sergei Prokofiev to a libretto by Sergei Prokofiev and Valentin Katayev based on Katayev's 1937 novel "I, Son of Working People" (Russian: Я, сын трудового народа… ).
 It was premiered on 23 June 1940 at the Stanislavsky Opera Theatre in Moscow.
Sergei Prokofiev's Piano Sonata No. 9 in C major, Op. 103 (1947) is a sonata for solo piano composed in 1947 and consists of four movements.
 The sonata was dedicated to Sviatoslav Richter, a member of the Union of Soviet Composers, and by whom it was first performed on 21 April 1951 in Moscow.
Sergei Prokofiev set to work on his Piano Concerto No. 2 in G minor, Op. 16, in 1912 and completed it in 1913.
 But this concerto is lost; the score was destroyed in a fire following the Russian Revolution.
 Prokofiev reconstructed the work in 1923, two years after finishing his Third Concerto, and declared it to be “so completely rewritten that it might almost be considered [Concerto] No. 4”; indeed its orchestration has features that clearly postdate the 1921 concerto.
 Performing as solo pianist, Prokofiev premiered this surviving “No. 2” in Paris on 8 May 1924 with Serge Koussevitzky conducting.
 It is dedicated to the memory of Maximilian Schmidthof, a friend of Prokofiev's at the St. Petersburg Conservatory who had killed himself in 1913.
Sergei Prokofiev's Violin Sonata No. 2 in D Major, Op. 94a (sometimes written as Op. 94bis), was based on the composer's own Flute Sonata in D, Op. 94, written in 1942 but arranged for violin in 1943 when Prokofiev was living in Perm in the Ural Mountains, a remote shelter for Soviet artists during the Second World War.
 Prokofiev transformed the work into a violin sonata at the prompting of his close friend violinist David Oistrakh.
 It was premiered on 17 June 1944 by David Oistrakh and Lev Oborin.
Sergei Prokofiev's Lieutenant Kijé (Russian: Поручик Киже , "Poruchik Kizhe") music was originally written to accompany the film of the same name, produced by the Belgoskino film studios in Leningrad in 1933–34 and released in March 1934.
 It was Prokofiev's first attempt at film music, and his first commission from within the Soviet Union; he had lived abroad since the 1917 October Revolution.
 After the film's release, Prokofiev adapted the music into what became a popular orchestral suite, his Op.
 60.
Visions fugitives, Op. 22, are a series of short piano pieces composed by Russian composer Sergei Prokofiev (1891–1953) between 1915 and 1917.
 They were premiered by Prokofiev on April 15, 1918 in Petrograd, Soviet Union.
 They were written individually, many for specific friends of Prokofiev's, and he originally referred to them as his "doggies" because of their "bite".
 In August 1917, Prokofiev played them for Russian poet Konstantin Balmont, and others, at the home of a mutual friend.
 Balmont was inspired to compose a sonnet on the spot, called "a magnificent improvisation" by Prokofiev who named the pieces ""Mimolyotnosti"" from these lines in Balmont's poem: ""In every fleeting vision I see worlds, Filled with the fickle play of rainbows"".
 A French-speaking friend at the house, Kira Nikolayevna, immediately provided a French translation for the pieces: "Visions Fugitives".
 Prokofiev often performed only a couple of them at a time as encores at the end of his performances.
Sergei Olegovich Prokofieff (16 January 1954 – 26 July 2014) was a Russian anthroposophist.
 He was the grandson of the composer Sergei Prokofiev and his first wife Lina Prokofiev, and the son of Oleg Prokofiev and his first wife Sofia Korovina.
 Born in Moscow, he studied fine arts and painting at the Moscow School of Art.
 He encountered anthroposophy in his youth, and soon made the decision to devote his life to it.
Konstantin Saradzhev (also "Constantin Saradgeff", born Saradzhian; 8 October 1877 – 22 July 1954) was an Armenian conductor and violinist.
 He was an advocate of new Russian music, and conducted a number of premieres of works by Pyotr Ilyich Tchaikovsky, Modest Mussorgsky, Igor Stravinsky, Sergei Prokofiev, Nikolai Myaskovsky, Dmitri Shostakovich, and Aram Khachaturian.
 His son Konstantin Konstantinovich Saradzhev was a noted bell ringer and musical theorist.