Doesn't work like that, There's no "this is your job, This is mine" Theres no black and white whose responsible for what as the two roles will always have an amount of overlap and situations are always so differnt and changing. It either works itself out or it doesn't and if your debateing who should be doing what then there's ya problem.
The co drivers never going to be in the right place all the time, The drivers not gona get it right all the time. . You need to adapt quickly to whatever your confronted with, Work well as a team and have an ability to know what each other are thinking without them saying anything.
Marshals shouldn't be doing anything other than making sure your within the rules and not doing anything dangerous. Even if your going about things in the wrong way aslong as its safe and inside the rules set out by the organisers they should let you get on with it.
If something does go wrong tho its ALWAYS the co drivers fault, Usually bad spotting