why are you installing extra relays? keep it clean, You only need one fuse before the main relay - branch a leg from the main to circuit opening relay, no need for fusing in between when you already fused the source.
10V at the pump will cause it to slow down and cause it to suck a lot of amps, sort it out, if you think the grounding is bad, run a ground from the pump wiring all the way to a good known grounding point in the car. Try adding a jumper to the ground pole of the pump and run it directly to the battery and see if the voltage changes, if it does not then your wiring from the relay to the pump is bad. Voltage measurement relies on two poles, negative and positive - if either is faulty you need to find that fault. Adding relays to the positive side wont ramp up the voltage.
For fuel piping, you need to buy a roll of steel tubing with minimum 8mm internal diameter and get a CNG technician to install it for you, you can then use small sections of rubber pipe to connect it to the pump, place a mercedes benz fuel filter inline (its quite big and high quality).
Do not rely on simple jubilee clips to hold the lines, buy some "band clamps" or look for an old mercedes mechanic and ask him for "mercedes ke screw vale pipe clip" - The have a screw and nut and tighten a band closed - they are not worm type. (google for Fuel injection hose clamp - they look just like them)
