I even connected the VIN on the 2nd arduino to the 5v on the first one.
That was a mistake, Vin needs to be about 7.5V in order for the regulator to work.
You should connect the 5V of the powered arduino to the 5V of the unpowered one.
I tired using a transistor to amplify the signal so the resistor wouldn't be a problem, which didn't help
Just one transistor will invert the signal you need two.