As Alex says - they are out of circuit.
It looks like this system was connected with the waste of the first membrane (at the bottom) going into the inlet of the next membrane.
So remove the red tube from the first membrane (at the bottom). Remove the red from the second membrane on the left and connected it to the first membrane. (You will have the waste from the first membrane going into the inlet on the second membrane. (The inlet is on the screw on cap.) Now do exactly the same from the second membrane to the third (top membrane) You will then need to connect the waste pipe with the restrictor and flush valve to the waste of the top membrane.
This will connect off of them up in series.