I agree with your post--while the scene at Sotherton is not ROTFLOL funny, it does have a wry sense of comedy about it. It is a serious subject, portrayed with a light and deft hand that I deeply appreciated. After the very serious tone in the opening chapters, JA demonstrates her incredible range and talent with this scence.

Your quotes and observations on the Bertram sisters are spot on. They were brought up to be well-mannered and to understand their duty, but not to have the kinder feelings that would make the performance of the duty a joy, rather than chore. Contrasted with Fanny, who finds happiness in the most mundane of tasks--such as being a companion to Lady Bertram, they appear to great disadvantage.

As far as the sisters go, competition amongst siblings is not uncommon...especially over male attention. I am not so surprised that Maria and Julia feel and urge to compete; what is surprising is that only Fanny seems to recognize how inappropriate Maria's behavior is. I was deeply disappointed by Edmund's observation in Chapter 12:

“Which is, perhaps, more in favour of his liking Julia best, than you, Fanny, may be aware; for I believe it often happens that a man, before he has quite made up his own mind, will distinguish the sister or intimate friend of the woman he is really thinking of more than the woman herself Crawford has too much sense to stay here if he found himself in any danger from Maria; and I am not at all afraid for her, after such a proof as she has given that her feelings are not strong.”

All I can say in defense of Edmund, is that perhaps he really has not spent much time in the company of women and therefore doesn't understand that Henry Crawford is nothing more than what we today would describe as a "player" using sibling jealousy to his advantage.