Duet book or pieces for adult beginner and teacher

[cdales]

Greetings! Just over a year ago, I launched a group for adult amateur pianists (https://www.meetup.com/Long-Beach-Piano-Meetup-Group/). I'm not a piano teacher, but rather a committed amateur looking forward to learning all those pieces I never got around to while earning a living  The group is successful beyond my wildest dreams, with almost 60 members who gather monthly (some have driven over 80 miles to join us!) to play, to collaborate with each other and the occasional guest string player, and to share triumphs and tragedies over food and drink. 
However, I would like to help beginners and/or early intermediates participate more fully in the group's activities. We currently have just one member who's been playing just over a year, and a couple more who are slightly more advanced. Can you recommend a favorite piece or book of pieces for four hands that a less advanced and a more advanced pianist could play together? I'm hoping for something that wouldn't require a lot of rehearsal so that I and othe pianists might be able to pick up the book and sight read our part during impromptu performances with the less advanced members. I've already looked over some of the Alfred duet books, but would love to tap the collective wisdom--all suggestions graciously received!

[aintgotnorhythm]

Good question, I would also be interested in any suggestions.

Other than something like the John Thompson piano course books (which have lots of intermediate level teacher piano accompaniments for the beginner part) all the duet books I have seen are more or less equal in level for both parts.