Shower Parts I Have A Shower With 3 Parts To Turn On And No Water Pressure Could This Just Be The Parts That Are Bad?

I have a shower with 3 parts to turn on and no water pressure could this just be the parts that are bad? - shower parts

I have 2 showers in my house 1 room has 1 Turn to be the shower and the other 3 bedrooms, 1 with Part 1 of a lot of pressure, but a can with 3 the pressure of the parties is bad or do that to worse be?