If you want them to eat more veggies, cut back on the jello shots. Offer those as a treat, same with the dried shrimp. I'd give them one or two every 2 weeks. You can entice them to eat the lettuce by rubbing turtle food on it or tuna juice, to give it an appetizing smell. Cuttlebone is common for birds - and it's the same thing as the "reptile cuttle bones". See if you can find a place that sells pet bird supplies. If not, sprinkling their pellets and lettuce with calcium can help. See if you can make "jello shots" from just lettuce. Carrot, tomato, and tuna should see moderate/rare usage, maybe once a week, or even less than that. Yes you can freeze veggies and let them defrost. Boiling them makes them lose a lot of their nutritional value. No, it's not bad for the turtles to wrap the lettuce in aluminum foil.
Usually, fish food is not designed to be the same as turtle food, as turtle food is usually higher in calcium. Take a look at this on the main RES page, if you haven't already:
http://www.redearslider.com/index_nutrition.html"Calcium content should always be offered in a greater quantity than phosphorus."