Triste No 3 from airs Nationals Argentinos, by Julian Aguirre  (1868-1924), for early intermediate Classical Guitar Duet (duo).
Pages: 7 pages both guitars with tablature, 3 pages Guitar I with tablature, 3 pages Guitar II with tablature, total 13 pages.
With standard notation and tablature, with downloadable mp3 for audio help, 2:50' min.

The Wearing of the Green is an Irish street ballad. It is to an old Irish air, and many versions of the lyric exist, the best-known being by Dion Boucicault (26 December 1820 18 September 1890).

For Flute and Guitar duet or Flute, Guitar and voice.
With melody line and lyrics.
With standard notation and tablature. With downloadable mp3 just for audio help.

Easy to early intermediate.
Pages: Three (3) pages (2 pages Melody/Flute and Guitar with tab, 1 page Flute part).

Take Me Home Country Roads, is a song written by Bill Danoff, Taffy Nivert and John Denver.
The song became one of John Denver's most popular and beloved songs.

Here is a version for Guitar duet and voice, with tablature, with melody line and lyrics, guitar chords.
Both guitars 9 pages, I guitar  5 pages, II guitar 6 pages, total 20 pages. Early intermediate to Intermediate.

Silent Night (Stille Nacht) is a popular Christmas carol, composed in 1818 by Franz Xaver Gruber. It was declared an intangible cultural heritage by UNESCO in 2011. The song has been recorded by a large number of singers (Bing Crosby, John Denver, Neil Diamond) from every music genre.
For Violin and guitar (fingerstyle) duet.
Violin Easy. Guitar Easy to Early Intermediate.
With downloadable mp3's for audio help (one with both the Violin and guitar and one with guitar only).
With guitar tablature. With melody line. With lyrics.
Pages: four pages (3 pages score, 1 page Violin part).

"Scarborough Fair" is a traditional English ballad that hangs in some versions at least upon a possible visit by an unidentified person (the "third party") to the Yorkshire town of Scarborough.
The song implies the tale of a man who instructs the third party to tell his former love, who lives in said fair town, to perform for him a series of impossible tasks, such as making for him a shirt without a seam and then washing it in a dry well, adding that if she were to complete these tasks he would take her back into his affections. Often the song is sung as a duet, with the woman then giving her sometime lover a series of equally impossible tasks, promising to give him his seamless shirt once he has finished.

Here is a version for Guitar trio with standard guitar notation and tablature. 9 pages all Gtrs, 3 pages Gtr1, 3 pages Gtr2, 3 pages Gtr3 - total 18 pages in landscape page format for easier interpreting.
With downlaodable mp3 for audio help.
Guitar 3 easy to early intemrediate, Guitar 1 and 2  (which plays the melody) easy.