The other point is HCPL-7520 primary side supply. I see, that you still didn't get the problem. The primary side supply has to be 5V, but the analog input voltage must be within the valid common mode range. Because it's connected to a shunt, it spans the full range of power supply C. As a consequence, Vdd1 supply must be floating, you'll need power supply "D" isolated from supply A - C. In my opinion, this requirement seriously questions the use of HCPL-7520 for the design.