The best way is to feed each microphone into a different analogue input via the appropriate coupling circuits and amplifiers of course.
However loudness is not always related to peak voltage so one way would be to integrate the signal.
As to direction, you might get some indication from the arrival times of the different microphones but this only works with impulse noises ( think bang ) and requires a faster A/D than you have built in to the arduino. However it is not very good.