All the hotels offer a buffet breakfast. For the evening meal, most hotels provide a buffet, so hopefully anyone with dietary requirements should be able to select items from the buffet. Please note that they may not have labels for the dishes though or a list of ingredients.
One of the hotels serves a set menu. They have indicated that they can provide for dietary requirements. It's worth bearing in mind though that from our experience, hotels in Turkey don't tend to be as used to dealing with dietary requirements as hotels in the UK.
In Istanbul, breakfast is provided at the hotel but not the evening meal, so you will be able to choose what you eat from the local restaurants.