I have never paralleled those meter shunts before like you are showing in your diagram. Don't be surprised if you get half the DC Current reading you are expecting...
Back in the day when we had multiple DC Meters to use we always put all of the DC Meters in series...
I would write down what it doing with only one meter set hooked up and see if it works OK for you paralleling in the second meter movement...
Only the DC lines between the Shunt and frame GROUND needs to be heavy duty wiring. Wires to and from the meter movement can be small wiring size..
Just saying from experience it may not work for you but give it a try anyway... If it doesn't work as expected you will want to leave the single shunt in place but wire the two DC meters in series coming off the single shunt.
Roy Ken
