My understanding of a continuous rotation servo is that when you send it the "position" value (as you would have for a normal servo), that value is direction and position together. Normal servos go from 0 degrees to 180, with 90 in the middle. For continuous rotation, 90 means stop, 0 is full speed one way and 180 is full speed the other.
So it's really no different from the normal servo code in the servo knob tutorial
: you control the continuous servo's speed and direction at the same time, just as if it was a normal servo's position.
Each axis of a joystick is just a potentiometer: so with an XY joystick you could control both servos from one joystick. Of course, you could use two if you want to, but you would only use half of each joystick: only one of the two axes.
Either way, you just duplicate the necessary parts of that linked code, changing and servo name and pin number where appropriate, for example:
Servo myservo; // create servo object to control a servo
int potpin = 0; // analog pin used to connect the potentiometer
int val; // variable to read the value from the analog pin
myservo.attach(9); // attaches the servo on pin 9 to the servo object
Servo myservo1; // create servo object to control a servo EDIT.... which is more or less what you posted meantime
int potpin1 = 0; // analog pin used to connect the potentiometer
int potpin2 = 1;
int val1; // variable to read the value from the analog pin
myservo1.attach(9); // attaches the servo on pin 9 to the servo object
// etc etc