When Bronn came in and threatened Jamie and Tyrion why did they not just shout GUARDS or when he was leaving get to the door and shout Guards arrest that man or are they that stupid in Winterfell that they let a strange man walk about with a crossbow and not be suspicious.
Really? If someone you believed would actually shoot you, had a gun to your head, you'd start shouting for help? You'd be dead very quickly...