Soak them overnight in penetrant and then use the biggest breaker bar you can find. 36 or 48 inch, usually 3/4 or 1 inch drive.
You could also try cutting a notch and using an air chisel to try and vibrate the rust loose while spinning the bolt.
Remember, left is loose, right is tight.
EDIT: Also, what impact are you using? Cordless half inch? Pneumatic 1 inch? What's its reverse torque?
Also, depending on how parts have worn, you can try using a floorjack under the wheel to try and relieve some pressure on the bolt. Not a lot of lift is needed, but sometimes bushings go bad and the suspension locks its own bolts in.