A PZM should work fairly well for that situation. The closer you can
get to the sound sources the better. One issue is that if you mount it
to the table any mechanical noises on the table could be transmitted
to the mic. If that's the case you could try the PZM on the cieling
but that would put it further away. You might also pick up a fair
amout of ambient sound such as HVAC etc. Ideally you would use lapel
mics on each person and a little mixer.