Processed American cheese like Kraft Slices and Velveeta are less desirable because they often contain starches and sugars and have a higher carb count than regular cheeses, but I do occasionally (like maybe once a week) use Processed cheese slices for things like scrambled eggs. Just count the carbs in your daily allowance.
String cheese sticks are usually slightly less than 1 ounce each, but just to err on the side of caution it might help if you counted each of them as 1 ounce and remember that during induction, cheese is limited to 3-4 oz. daily.