[lil fu fu girl]

Apples are fine for dogs whether with the skin, or without, depending on whether they are organic or not.( Non-organics are sprayed with pesticides that remain within the skin.) Apples contain valuable fiber and vitamin C, both of which are required for healthy pets. Apples are also high in omega 3 and omega 6 fatty acids which promote healthy coats in our pups. Clinical research has also found that apples are involved in controlling skin allergies.

The only part of the apple you must not give, is the core and the seeds as they do contain cyanide.

As you stated, they do contain carbohydrates( ~ 16 g /apple), but the amount you are giving them (16/4=4gram which roughly equals around 16Kcal.) is not very much.

As long as your dogs are not showing signs of GI upset, through diarrhea and vomiting, I would say, continue letting them have their healthy special treat.