I am not an expert about etiquette of the time, but I was rather surprised that mrs Dashwood, a widow lady with 3 young daughters and no male relative living with her, invites a young bachelor like Willoughby to stay with them in the cottage? I would have said that it was rather improper since she woudl have no male host to receive Will? I know that they have edward to stay, but he is a sort of brother in law....I would have thought that it would lead to gossip - "there's Mrs Dashwood, a still young widowed lady, and her 3 fairly nubile young daughters and they have a young man staying with them... under the same roof, and in a very small cottage....
Perhaps if it were a large country house it might be different as W could be given a bedroom miles away from the ladies' accommodation... but in a little cottage?
or would mrs D's married and then widowed status mean that she would be an adequate chaperone?