Hi, @tocco
Welcome to the forum.
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Do you have a DMM to measure the 5V on each of the Nanos.
If you just have one egg unit powered up, does the fault still occur.
A thanks for the informative pics and description of your project. 
A more informative schematic would help with pin numbers and hardware labels.
Just draw a couple of LDRs and label the other inputs to the Nano that they are from the other LDRs in your project.
What communication system are you using between the Mega and the Nanos.
If RS232 the Mega only has 4 UARTs, are you using software serial library as well?
Thanks.. Tom... 
