I agree, I also cannot see how anyone can be certain Crispy wouldn't have barked his head off if anyone climbed through the window in the middle of the night.
Does anyone know where crispy used to sleep? If he slept in the bedroom with June and Nevill he may not have wakened, he was an old dog so his senses may not have been too good. I tend to think he was more likely to have slept in the kitchen near the Aga but have never seen a dog's bed in any of the photos??
Dogs want to be near their masters, he likely slept on the bed or at least in the master bedroom. This is especially the case with a lone dog which sees the people as his pack. Only when dogs are caged and the cages are some other location than a bedroom will they sleep away from their masters. I have little doubt Crispy was in the master bedroom and until Jeremy went in the bedroom and woke up everyone he would not have known he was even in the house.
As for the other dogs they were in outbuildings so would not even have any reason to bark.
Loud noises like gunshots usually scare dogs so they go hide.