You don't have to remove the belt to get to the back one. Not so sure about the front one, but I will have a look in an hour or so - I have a 2.8 in the workshop
Those codes don't appear to be faults with the sensors though - they are usually specific, something along the lines of "camshaft position sensor G40 open or short to ground". They sound more like the ECU knows the cam adjustment isn't adjusting properly, as it can measure that with the position sensors. If both sensors had failed it wouldn't run at all, as the ECU would have no idea what the engine was doing.
Are you using VCDS or a generic scanner though?