Your code looks OK
analogWrite(en1Pin,70); //speed A
analogWrite(en2Pin,100); //speed B
digitalWrite(in1Pin,LOW); //1-2 run at speed A
digitalWrite(in2Pin,HIGH);
delay(1500);
digitalWrite(in1Pin,LOW); //1-2 stop
digitalWrite(in2Pin,LOW);
digitalWrite(in3Pin,HIGH); //3-4 run at speed B
digitalWrite(in4Pin,LOW);
delay(5000);
digitalWrite(in3Pin,LOW); //3-4 stop
digitalWrite(in4Pin,LOW);
digitalWrite(in2Pin,LOW); //1-2 run at speed A
digitalWrite(in1Pin,HIGH);
delay(1500);
digitalWrite(in1Pin,LOW); //1-2 stop
digitalWrite(in2Pin,LOW);
I have annotated it to help me understand what I think you are trying to do
Can you confirm that the names you have given the pins correspond to the actual inputs on the H bridges ?