I would try to put the drumset in a booth, as well as any other percussion - with mics 3 or more feet from the marimbas (and up to 7 marimbas) you'll want to minimize that bleed. Depending on the music, you might be able to keep the marimbas in one room, perhaps in a semi-circle...
I have gotten the best results (that the artists were happiest with) using large diaphragm condensors or tubes. A few favorites have been U47s, U67s, TLM170s, M147s, UM70s. I have used small di a few times, but have found them lacking a little in the 'beefier' tones - again this may depend on the music. I plan to try a pair of DPA 4011, have used 'lesser' small di in the past.
If they are 'two mallet' players, you may get away with one mic per instrument (if they confine themselves to a small section of the scale for each song). If they are 'four mallet' players, or using the whole instrument, which is large, I'd suggest two mics. I have used X-Y, but it tends to make the center too strong (and it's the strongest part of the instrument anyway). So, spaced pairs are the best bet, using careful placement to avoid phase issues... Also, keep in mind that directly adove the keys might give you too much resonance from the resonators. You might need to back off or angle the mics a bit...
Good luck...