Just remember that with a pneumatic system, the pressure applied will be depending on air pressure, area of cylinder and amount of friction of the rod.

The friction represents how much excess pressure that is needed to move the rod. So if the friction is suitably low, then a single air pressure sensor would indicate the pressure for all measurement tips with the exception of tips that have reached the end limiter.

So depending on how exact you need to measure the tip pressure, you could get away with a single air pressure sensor. It's just a question of if all your rods have a suitably low friction. On the other hand - the position sensors needed in the system will be able to detect at what air pressure the rod will start to move. So you could get some individual calibration that way.