I'm new to all of this as well but I will say that you should probably cut back their food (because of the pyramiding) do you feed them each a head size every other day? or daily? I read on the site that once they are a year old they need to be fed every other day. Overfeeding can lead to a lot of problems. (p.s. I know the begging is insane and irresistable! I'm having to deal with that myself! it's haaard!

) I found that offering romaine lettuce ,or any veggie on the list under basic care, every day helps because you can never feed enough veggies and if they like that particular veggie, they'll turn to that when they don't have the pellets! They're like bottomless pits!

Also if you have 2 7inch turtles-- 29 gallons is way too small and even 55 gallons is too small! as big as they are now you would need a 140 gallon tank or pond (10 gallons per inch) and depending on whether they are male or female you may need even more space then that! Females can get up to 12 inches- and from the looks of it you may have a female on your hands because the claws are very short!!
You say you had gone to a vet and were told the turtles were fine? was this problem occuring when you took them then? is that a sore on your turtles right arm?
I'd recommend reading the basic care if you have not already!