IMO, I think their lack of retaliation has got a lot to do with the fact Nicola and Miranda regard Wendy Tredgold as common. To reply would be to lower themselves to her level. Plus I think that in their times, overt verbal aggression would have been rather less frequent than it is today - they are observing the mode of conduct of their world. Which isn't in the least to say that no aggression is ever displayed at Kingscote...