What kind of music is it--classical, jazz?
What kind of the room, and how the pianos gonna be positioned--'wing to wing', or 'keyboards on the line'? In the first case you might need to take the lid off from one of the pianos, or use one fig 8 (if you can get hold of it) for both pianos. In the second case, you won't need a baffle, as the open lid of the 'front' piano will be a 'natural' one. Are the pianos from the same brand? How different is their sound? Obviously, if you mix Yamaha and Steinway, for example, you will need to mic them for the closest sound possible. Usually, in classical piano duets you want to blend (that how pianists like it to be) both pianos as much as it is possible. Also, keep in mind, that you will hear very nice sound of 'turning pages', if the pianists play with a score-- advise them to make zoomed out photocopies, so more pages could fit on the music rack.
Give more information.

it is classical piano. the room is really good with a vaulted ceiling. the pianos are going to be positioned beside each other i guess "keyboards on the line" taking the lid off is not an option. the pianos are not of the same brand one is a steinway and one is a baldwin, possibly a yamaha. I can't remember. In any case they do sound different. they have memorized their pieces so turning pages wont be an issue.

Since the pianos are different, I would try to make a similar tonal balance, first. The instrument with more projected sound put as a 'front' one. Since you will probably need a distant micing, let 6-10 feet between the pianos. Listen to the instruments and try to decide which one has brighter or darker sound. With brighter piano place your mic closer to the bass strings side, with darker, to the highs. Also, try to tilt the mics towards strings for less projected instrument, and open lid, for more projected one. In short, with micing try to equilze the sound as close as it is possible, then take care of the rest with EQ. Actually, for the close mics I would try your SD cardioids first, and use omni pair with 4033 center mixed to two tracks, as a room reverberation, but you will need to experiment.

Of course, the pianos should be tuned against each other, otherwise it will sound like... J.Cage 1/4 tone pieces. But I am sure you know that.

I cannot give any recording advice though I know how difficult it is to match piano sounds unless you have an assortment of instruments to choose from and a good technician able to find a happy medium. I once played Ives 1/4 Tone Pieces [Cage was the prepared guy] with one nice Hamburg 9 ft. and a beat up NY 9 ft [with a dull but still rather clangorous sound]. Yuck! Piano condition will play a large role in the overall sound.

Best of luck!

I once played Ives 1/4 Tone Pieces [Cage was the prepared guy] with one nice Hamburg 9 ft. and a beat up NY 9 ft [with a dull but still rather clangorous sound]. Yuck! Piano condition will play a large role in the overall sound.

Of course, you are right, Coats--it is my dislexia... I played Ives' three 1/4 tone pieces myself in the concert. It was a very funny experience, btw. We always rehearsed it on normally tuned pianos, and then, only on the day of the concert, the second piano was tuned down. The dress rehearsal was a nightmare. I just could not understand where I am and what is going on! You know, it is like to get wrong glasses. Anyway, it is very cool music.

Marik,
That would be difficult! The newly tuned piano probably wouldn't hold it's first tuning for that long. Ours were tuned 3 times within a week and still had trouble staying in perfect 1/4 tones.
I've played Mozart concertos with 2 pianos in better quarter tone tuning, without the tuner even trying!