I am sorry so will try to rephrase
Well we are getting closer but it sounds even more weird.
Arduino nano is being turn on and off by the Arduino Mkr1000 via transistor (the entire board not just the i/o)
To quote a famous tennis player "you can not be serious!"
Have you taken into account that when this powers up it will go into boot mode for several seconds where it could latch up.
Have you taken into account that when this powers down it could be being phantom powered if signals are still being fed into it and therefore not being off at all?
Am I right in thinking that you have four Processor boards? Your list says so. But your description only mentions one node MCU, not two.
So one end of the data cable goes there[Nano]
Don't cut it in a circuit that no one but you has seen. We don't know a lot of things like do all processor boards share a single ground? What are the decoupling capacitors and how are they arranged? Do you use a series resistor in the data line?
I know that it is a typical beginners response to try and use two processes to cover up the fact they can't program, but using three or four is just being silly.
When trying to attach the wiring diagram it just says the was a problem uploading the "name of the file"
Is this a file that is on your computer? It needs to be and not a link?
Is this a jpg or png file?
Is this file smaller than 2M?
After writing the above I looked at the latest link.
Now it so happens I have a drop box account and I managed to download your image and find it is 11.1M in size. So that would be over 2M then.
So I converted it to a jpg file and that come in at 1.5M which is under 2M.
So I can post it here.
I must say that it seems not to be worth the effort, there is lots of information missing.
What FETs are these, part number?
The source and drain seem to be connected to ground?
That is never going to turn anything on and off.
You don't seem to have ANY capacitors!
You don't show how anything is powered.
You show a symbol for ground but also use GND as a label, are these the same points?
You show three processors but you had four in your list.