We find shorter pieces go down better, for 4 hands 1 piano try;
Capriol suite - Warlock
polonaise militaire - Chopin (arr. Gheel)
Sheep may safely graze - Bach
Deutsche Tanze - Beethoven
Waldstain variations - Beethoven
Sonatina - Weber
petit mari, petite femme - Bizet
Cradle song - Arensky
Badinage - Rowley
Tritsch-tratsch polka - Strauss
Norwegian dance - Grieg
St Antoni chorale - Brahms
Sonatina Op. 17 - Kuhlau
Minuet favori - Mozart
Finally, if you have another friend, try The Secret by Gautier (arr. Gurlitt), 6 hands, 1 piano!