Hi there!
I looked up the tech specs for the Nano board you are using. It says that out of the 22 digital pins, six of them can use to send a PWM signal, which is a way to get an analog voltage out of a digital pin. With most Arduino boards that have six of these PWM pins, such as your Nano, pins 3, 5, 6, 9, 10, and 11 are the six pins listed as PWM pins. I see in your code that you have pin 8 attached to your second servo, which is not a PWM pin. Instead of pin 8, try again using pin 6 and let me know.
As for why the second potentiometer value is not being used as you want, I'm not entirely sure yet.
Can you also upload a picture of your setup with wirings and everything?
Thanks