using 2 linear regulators and power half the devices with other and the other half with the other.
This should work just fine.
also what is the chance one of these will break and surge 12 volts through my 100's of dollars in sensors and Arduinos?
They usually break because the load (current) is more than they can source (check the datasheet).
From what I reckon, a broken regulator would not provide any voltage (rather than allow the input voltage to go through).
You can get a 5V/3A switching mode regulator on ebay for $5 or less.