Are you feeding mice or rats? I'm assuming your feeding f/t because of the assisted feedings, but have your tried offering them live? Assisted feedings are stressful, but force feedings are even worse. Have you double checked that your setup is correct? I would probably also take them to the vet at some point if they don't start taking food on their own soon. It's possible they have some internal parasite or are sick. You don't want to have snakes you have to force/assist feed for the next 30 years. Some babies are small, but if they haven't been gaining weight I would definitely take them to the vet.