Webby was a much later addition, and belongs strictly in the 'DuckTales' series - April, May and June are Daisy Duck's nieces, similar to how Huey, Dewey and Louie are Donald's nephews. (I'm not sure whether they live with Daisy or not - I've never seen them depicted as doing so.) And this sort of thing was par for the course with the boys - one of HD&L's primary flaws is that they REALLY dislike girls, in the 'Eww - cooties!' sense. In an early Barks ten-pager, the boys are aghast to learn that (as they put it) "G-G-GIRLS!" are competing against them in a kite-flying contest. "If a girl wins this contest," they moan, "this town won't be fit to live in!" Take from that what you will.