Well your sister shouldn't be upset with the pits. They were only reacting to Stevie's behavior and actually did well with only reacting after a second nip by Stevie. I would say it was a bit naive of Grandpa not to have noticed the large dogs in the yard but that's a lesson learned. It's a blessing that Stevie will be okay but he was the fuel that started this fire. I can understand the hurt in this situation but the pits aren't at fault and shouldn't be condemned or hurt.
Troy and I have visited my brothers house before and Troy has Little dog syndrome and doesn't like big dogs. My brother had a pit puppy, not much bigger than Troy at the time but I knew the dog had a good 7 pounds on him and that he could still hurt him even though he was just a puppy. Even though small dogs seem like a lot of low maintainence, they are high maintenence when it comes to protecting them when they can't really protect themselves when they think they can.