Is it possible to control the speed of DC motors with Arduino's analogWrite() using analog pins?
No, you can't.  As it says in the Arduiuno reference page for analogWrite(): "The analogWrite function has nothing to do with the analog pins or the analogRead function."

You can use the "analog input pins" (A0..A5) of Arduino for analog input, or as digital inputs or outputs.  They cannot be used for PWM(digital)-output.  Only digital pins, and only those specifically stated for PWM-output, can actually be used for PWM output (unless you go down the path of software-PWM, though I would hesitate to do that for an H-bridge).