More multi-song juxtapositions that spring to mind:

Leonard Bernstein: "A boy like that/I have a love" - from WEST SIDE STORY

Irving Berlin: "Play a Simple Melody" - used in the movie GIVE MY REGARDS
TO BROADWAY (start watching at 2:05 -

Stephen Schwartz: "All for the Best" - from GODSPELL

Joe Brooks: "It's Only Love/Bring on the Night" - from METROPOLIS (This is a
truly beautiful two-song juxtaposition from an otherwise dire musical.)

Boublil and Schoenberg: "One Day More" - from LES MISERABLES

Sondheim: "Now/Later/Soon" - from A LITTLE NIGHT MUSIC

Sondheim: "Johanna" (reprise/quartet) - from SWEENEY TODD

Vocal/Instrumental Juxtapositions

J.S. Bach/Gounod: "Ave Maria" (juxtaposes Prelude No. 1 from Bach's
Well-Tempered Clavier juxtaposed against Gounod's original "Ave Maria" setting

Beethoven/Gesner: "Schroeder" - from YOU'RE A GOOD MAN, CHARLIE
BROWN (juxtaposes the first movement of Beethoven's Moonlight Sonata
against an original song by Gesner -