For part (b): does this mean that each robot can contain only one 12"x12" sheet worth of self-fabricated steel or aluminum? Or, can we only use one sheet between both robots? Or, can we use as many sheets of Steel/Aluminum as we want, so long as it doesn’t start at greater than 12"x12"?
I am not in VEXU so feel free to correct me but in VRC HS/MS the non shattering plastic rule looks similar to the steel or aluminum sheet rule which to my interpretation means you can’t use more than just one sheet to cut from. In the first line of VUR2 says for each robot so I would interpret that as one sheet worth per robot
Hope this helps and again feel free to correct me
I concur with your assumption but I was hoping for more unanimous agreement so I knew how to proceed 
Single sheet per robot. All parts had have been able to be fabricated from a single sheet. If multiple complicated pieces were used I would suggest a diagram to show how the sheet could have been cut.
5 robots can each contain their own sheet