Using Two Arduino to Lower Power Consumption
I would do as follows:
Software:

Arduino is in sleep mode

every x seconds (x depending on your needs), wake up then switch on and read one sensor after the other and transmit the results or whatever you want to do.

then go back to sleep


Hardware:

as you have 4 sensors, you can connect their outputs to the arduino analog inputs (or digital...)
you will need 4 electronic switches, preferably Mosfets, connected to 4 digital outputs to switch the power of each sensor independently

This should reduce the consumption to the minimum.
Once your system is running, you may also think about using only the AVR microchip, not the complete Arduino, e.g. If you don't need the USB connection. In addition, you can further reduce consumption by clocking the AVR chip to a lower clock, if not using Arduino.