As L4 stated the kitties' diet needs to be changed to eliminate the dry food all together. All of the diet changes will play havoc with your kitties' bellies. Sort of like when we eat too many veggies or too much fruit. And we are built to handle that type of food. Cats aren't. Cats are obligate carnivores. They need meat, not grains. Deworming again wouldn't hurt.
Once the kittens are on a good diet and not yoyoing back and forth I am sure things will improve. Please don't expect overnight though. It will take a while for the bellies to settle. Meanwhile you could try adding some probiotics to their diet. It will help rebuild their belly flora. You can find probiotics at most health food stores and good pharmacies.
Please try to find a Global pet food store or even Pet Valu. Their food choice is much better quality than the food mentioned.