yes you can sell the car while still paying for it. you have to check the market value of the car. you sell the car what ever price you want. then you pay the bank the money you owe keep the rest of the money.
Yes and also be sure to be open about money being owed on the car as people often do checks on the rego, and if they find money owing on it they will run for the hills if you have not disclosed the issue.