] They were raised by the same mother, so from where does she get her good sense? We can guess from the father, but we don't really know.

Good question: I find that from a modern perspective, neither heredity nor up-bringing seem to play much of a role in JA's novels in general. There's no telling where Elinor got her good sense from, with such a charming but rather irresponsible mother (and a father who, as others have pointed out, quite possibly wasn't a model of responsibility either), or why Edward turned out to be a decent person when he had such an awful family. It seems to me that JA's heroes and heroines are superior just because they are, not because anything made them that way. (Actually, this would be a good thread for Austenuations - I think I'll try it there!)