Question: Who did the choral arrangements of Across the Universe, The Long and Winding Road, and I Me Mine?
About the article "Let It Be", section "Personnel".

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The Beatles
George Harrison – lead and rhythm guitars, acoustic guitar on "For You Blue" and "I Me Mine", tambura on "Across the Universe", tuned-down six-string electric guitar on "Two of Us" and "Maggie Mae", lead vocals on "I Me Mine" and "For You Blue", backing vocals.
John Lennon – lead and backing vocals, rhythm guitar, lead guitar on "Get Back", lap steel guitar on "For You Blue", acoustic guitar on "Two of Us", "Across the Universe" and "Maggie Mae", six-string bass guitar on "Dig It", "Let It Be" and "The Long and Winding Road", whistling on "Two of Us".
Paul McCartney – lead and backing vocals, bass guitar, acoustic guitar on "Two of Us" and "Maggie Mae", piano on "Dig It", "Across the Universe", "Let It Be", "The Long and Winding Road", and "For You Blue", Hammond organ and electric piano on "I Me Mine", maracas on "Let It Be".
Ringo Starr – drums, percussion on "Across the Universe".
Additional musicians
Richard Anthony Hewson – string and brass arrangements on "I Me Mine" and "The Long and Winding Road"
John Barham – choral arrangements on "Across the Universe", "I Me Mine" and "The Long and Winding Road"
George Martin – shaker on "Dig It", string and brass arrangements on "Let It Be", production
Linda McCartney – backing vocals on "Let It Be"
Billy Preston – electric piano on "Dig a Pony", "I've Got a Feeling", "One After 909", "The Long and Winding Road", and "Get Back", Hammond organ on "Dig It" and "Let It Be"
Brian Rogers – string and brass arrangements on "Across the Universe"
Production
Glyn Johns – audio engineering, mixing
Alan Parsons – assistant engineer
Phil Spector – "re-producer" (final overdubs), final mixing
  "Get Back" (John Lennon/Paul McCartney) – 4:25  "Two of Us" (Lennon–McCartney) – 4:04  "Dig a Pony" (Lennon–McCartney) – 4:40  "I Me Mine" (George Harrison) – 4:41  "Across the Universe" (Lennon–McCartney) – 4:15  "Dig It" (Lennon–McCartney/Harrison/Richard Starkey) – 1:32  "I've Got a Feeling" (Lennon–McCartney) – 4:34  "The Long and Winding Road" (Lennon–McCartney) – 1:49  "One After 909" (Lennon–McCartney) – 3:20  "For You Blue" (Harrison/Hardin) – 5:10  "Maggie Mae" (Auf der Lüneburger Heide & Was gleicht wohl auf Erden)" (composed by Ludwig Rahlfs with lyrics based upon a poem by Hermann Löns) – 3:41 Track listing.
"Across the Universe" and "I Me Mine" are incorrectly listed on the CD packaging — their order is swapped. 
 "Get Back" (LP version) "Don't Let Me Down" "The Ballad of John and Yoko" "Across the Universe" "For You Blue" "Two of Us" "The Long and Winding Road" "Let It Be" (LP version)  
 Paul McCartney – lead vocals, piano John Lennon – bass George Harrison – lead guitar Ringo Starr – drums Billy Preston – Hammond organ Personnel.
Uncredited – Phil Spector's orchestral and choral arrangements 
During this period, Barham met George Harrison of the Beatles through Shankar, who had adopted the guitarist as his sitar student.
Harrison was fascinated by Barham's interpretations of ragas, and based his 1967 song "Blue Jay Way" on a piano piece that Barham had derived from Raga Marwa.
In March 1967, Barham attended the recording session for Harrison's Indian-styled composition "Within You, Without You", released on the Beatles' seminal album "Sgt.
Pepper's Lonely Hearts Club Band".
Barham later wrote the choral arrangements for Phil Spector's controversial production of "The Long and Winding Road" and "Across the Universe", issued on the band's final album, "Let It Be" (1970).
Several commentators credit Harrison as the person most responsible for Indian music's surge in popularity in the West from 1966 onwards, via his work with the Beatles and his public endorsement of Shankar.
Among these, author Simon Leng has described Barham as both a "birth partner" and the "closest confidant and fellow traveler" to Harrison during the latter's immersion in the genre.