One of the most special things that my husband and I do together is playing piano duets (sometimes organ/piano duets). I don't personally know very many musical couples; we consider it a gift from God to our marriage, and we love being musical together. I have to say- it has never been an issue of competition either. It is something we truly enjoy and love about each other.
But just like learning the piano is an art, so is learning to play with someone else! It takes a lot of coordination and teamwork. Teacher/student duets are fun, as are friend/friend duets. :) I have always found it easier to play with my husband because we are used to each other, and we think a lot alike. I feel a bit more nervous if I'm teamed with someone else. But it can still work! Here are some pointers:
Two Pianists/One Piano:
*Choose a piece of music that is doable for the level of both pianists. (If one pianist is a few levels below the other one, choose a song from the lower level).
*Practice your parts separately before trying to put the duet together. This will avoid certain disaster. :)
*Decide who will work the sustain pedal, and discuss and practice the places where there are specific pedaling needs. (Sometimes the person who controls the pedal may not need to pedal in a certain measure, but their partner has a measure where they need extra or specific pedaling.)
*Decide who will turn which pages, based on who has a hand free when the time comes. (In some songs my husband turns all the pages, and in other songs I do some and he does some.)
*Practice counting out loud to lead yourselves into the song at the same time. When the actual performance time comes, count under your breath with each other before beginning to play.
*Practice trouble spots often (and usually the same spots will pop up.)
*Pay special attention to hand crossings and tricky finger sharing places.
*Practice the end of the song until you are lifting off the keys at the same time.
*Practice in the presence of someone with a good musician's ear, and ask them if the duet sounds balanced, and if the melody is prominent throughout the song.
*HAVE FUN! :)
Two Pianists/Two Pianos (or One Piano/One Organ):
* Use the guidelines that apply from the above pointers
* If possible, position the instruments so that both musicians can see each other.
* Discreetly nod or count (moving your lips) with each other at the beginning and end of the piece, so as to start and finish at the same time.
* Let the person who carries the melody have the greater volume. (This may change several times during a piece, so adjust your volume accordingly.)
* Write down the organ settings on your music (instruments, master volume, sustain, pedal volume, etc.) Then the next time you play that song, you will know what settings to use. (Also, if little fingers have changed the organ settings since you last played, you can re-set it without too much trouble)