67 Camaro has been sitting, Should I replace the brake lines ?
Or tips on cleaning them out ...

 

Sitting how long? Honestly if you don't know how old they are I'd want to replace them anyway but if the car has been sitting for a number of years it's a no brainer replace them. Low cost to do and a major safety factor,same goes for the tires.

 

Are you talking about the metal lines? Of course if they are rusty they should be replaced. If you run mineral sprites through the lines and it is clean with no rust it should be ok assuming they are not original. All the soft lines should be done so you know the age.