arduino due control ai motor's

Dear friends,
My use arduino due I / O for TX0 & RX0
Here is my program

int led = 13;
int id;          // 馬達ID
int torg;        // 轉距(0:max, 4:min)
int checksum;    //  通訊協定
int tmp1, tmp2;  // byte  數量

void setup()
{
  pinMode(led,OUTPUT);
  Serial.begin(115200);  // 起始串列115200bps
  while(!Serial){        // 等待通訊
    ;
  }
  id = 0;
  torg = 2;  //  轉距速度
  
  digitalWrite(led,HIGH);
  tmp1 = (torg << 5) | id; //  馬達速度及編碼號
  tmp2 = 60;  // 位置碼
  checksum = (tmp1 ^ tmp2) & 0x7f; // 結束碼(馬達速度及編碼號XOR位置碼)
  Serial.write(0xff);   // 回傳編碼
  Serial.write(tmp1);
  Serial.write(tmp2); 
  Serial.write(checksum);
  delay(5000);   // 等待時間
}

void loop()
{
  digitalWrite(led,HIGH);
  tmp1 = (torg << 5) | id;   //馬達速度及編碼號
  tmp2 = 100;   //位置碼
  checksum = (tmp1 ^ tmp2) & 0x7f;  //結束碼(馬達速度及編碼號XOR位置碼)
  Serial.write(0xff);   //回傳編碼
  Serial.write(tmp1); 
  Serial.write(tmp2); 
  Serial.write(checksum);
  delay(1000); //等待時間
  
  digitalWrite(led,LOW);
  tmp1 = (torg << 5) | id;
  tmp2 = 200;
  checksum = (tmp1 ^ tmp2) & 0x7f;
  Serial.write(0xff);
  Serial.write(tmp1); 
  Serial.write(tmp2); 
  Serial.write(checksum);
  delay(1000);
  
  digitalWrite(led,HIGH);
  tmp1 = (torg << 5) | id;
  tmp2 = 180;
  checksum = (tmp1 ^ tmp2) & 0x7f;
  Serial.write(0xff); 
  Serial.write(tmp1); 
  Serial.write(tmp2); 
  Serial.write(checksum);
  delay(1000);
  
  digitalWrite(led,LOW);
  tmp1 = (torg << 5) | id;
  tmp2 = 220;
  checksum = (tmp1 ^ tmp2) & 0x7f;
  Serial.write(0xff);
  Serial.write(tmp1); 
  Serial.write(tmp2); 
  Serial.write(checksum);
  delay(1000);
}

Ai motor have four pins inside the motor (V, TX, RX, G)
Motor TX → DUE RX0
Motor reception → DUE TX0
AI motor it can control, but not control another one
How do I modify my program use to DUE another pin for TX1, RX1, TX2, RX2, RX3, TX3 (pin)
I have 4 AI motor control

How to do modify to control 4 ai motor and use all TX RX pin?

How do I modify my program use to DUE another pin for TX1, RX1, TX2, RX2, RX3, TX3 (pin)

What have you tried? If Serial talks to TX0 and RX0, what do you suppose that Serial1, Serial2, and Serial3 talk to?