These three measures are independent of each other. The maximum feed pressure is the maximum pressure exerted by the pump to push water through the system.
Backwash pressure is the maximum pressure exerted by the pump during backwashing to push water through the system. The pump operates at a higher feed rate during the backwash.
Transmembrane pressure is the pressure exerted on the water as it moves across a membrane. It is determined by the resistance that the membrane provides to the water.