Control FDC3260 through Arduino Due

Hello,

I am using 2 FDC3260 controllers to control 6 nos. of Parker EHA model no. 649202. I am doing it through Arduino Due. For that, I attached RS232 and 'RS232 to TTL' converter to feed the commands from the Arduino. The 'RS232 to TTL' connected to Rx1 & Tx1 of the Arduino is considered Serial1 and 'RS232 to TTL' connected to Rx2 & Tx2 of the Arduino is considered Serial2. I have not found detailed documentation about the control FDC3260 or similar controller through Arduino Due I want to implement.

My question is are the following commands good to move the EHAs:

  Serial1.println("!g 1 " + String(100));
  Serial1.flush();
  Serial1.println("!g 2 " + String(100));
  Serial1.flush();
  Serial1.println("!g 3 " + String(100));
  Serial1.flush();

  Serial2.println("!g 1 " + String(100));
  Serial2.flush();
  Serial2.println("!g 2 " + String(100));
  Serial2.flush();
  Serial2.println("!g 3 " + String(100));
  Serial2.flush();

Do the 1, 2, and 3 numbered motor channels in each controller corresponds to "!g 1", "!g 2", "!g 3" respectively?
What is the maximum and minimum value I should use in place of 100 for better and more efficient control? I am using 6 EHAs to manage a plate connected to them with spherical joints, so the movement of each EHA must be under control so that none of the extension or retraction makes the movement of the plate out of balance and breaks any of the spherical joints. 

To maintain the height of the EHA pistons to some predefined values, I am using the PID control library in my Arduino code.

I am not getting good results in the motion control as the movements of the EHAs are not in sync. The PID controller controls the value 100 and sometimes they fall so less with respect to others, the system experiences imbalance and takes several minutes to reach the desired actuator length.

Anyone can suggest any better and more efficient way to control the controllers through the Arduino?