Can I connect multiple devices via a single I2S interface?
As the microphones are clock slaves and can be configured to be either left or right channel on a standard stereo I2S bus, you can connect two microphones to one I2S input peripheral that is the clock master.

Which means four mics can be connected to two I2S interfaces, as long as both have I2S data inputs. Both I2S peripherals can be clock masters, but if you want clocks to be in sync, one of them can be clock master and other can be clock slave.