When the elder Mr. Dashwood dies, John and Fanny have been married at least five or six years since young Harry is four. By this time Fanny has had plenty of time to improve on John's substandard/imperfect cold-heartedness and selfishness. With Fanny's coaching during the years of their marriage, John is probably predisposed to be talked into giving his mother and sisters nothing. "This argument was irresistible. It gave to his intentions whatever of decision was wanting before; and he finally resolved, that it would be absolutely unneccessary, if not highly indecorous, to do more for the widow and children of his father, than such kind of neighbourly acts as his own wife pointed out." Ugh!