Aquatic turtles shedding small pieces of their skin is not uncommon, nor is shedding their scutes as they grow. However, it can be also be a response to avoid infection or a water quality issue.
Be sure they both have adequate climbing spots to get out of the water. They are not really "baskers" like other water turtles, so your heat lamp may be a bit too much. You have not provided the temps of your tank where the heat lamp is.
They also need a more diversified diet than just reptile sticks. These are snappers! You haven't said how old or large (in terms of inches in length) they are, but snappers are carnivorous .. even the young ones. Reptile sticks ain't gonna cut it, they need live food and they need protein.
I'm sure you are aware how large they grow and how long they can live. That is a big big commitment. Not trying to sound preachy, but I took in a "pet" common snapper that the owner no longer wanted as it got too large. Took me over a year to reacclimate it to the lake behind my house.
My only other encounter was when I found an adult common in my front yard years ago and thought what a great educational tool for my young boys. Put the snapper in a big, big tub and kept for a couple days, teaching my boys. Then I decided to take him out of the tub to release back to the lake. I held him under the front and back carapace, fully aware of his long neck and attitude, lol, and talking to my boys the whole time; the next thing I knew his back right leg nails ripped open my right arm under my wrist. I thought they could not do that if I held properly! 28 stitches later I was good and my boys were highly amused. Just be aware that there are better turtles to make pets. Best of luck to you and the turts
