My thoughts...
Sybil was a protective and caring mother who was torn by the fact that she was leaving her family way before she should have due to a debilitating illness.
Amy was unhappy because she wasnt with the one man she truly cared about (Brad) they weren't together and she has regretted it and has been sad/pissed off at the world ever since.
Everett was torn because he grew up and thought Meredith was the kind of person he should be with even if he didn't love her because it would make his mother happy that he found someone and just might "cure her" of her illness.
I LOVE this movie for its wit and candor and honest feelings on other people especially new comers who make their way into the family. It's raw and its how some people really feel when their oldest son/brother or anyone brings someone into their lives that may be a mistake or in some ways, an unseen blessing. I can't believe that all every one sees from this movie is the negativity and none of the underlying messages and truth to it all!!! I repeat, I LOVE THIS MOVIE!!!!
So that is my take on this movie. It can be harsh, but it is honest and in some cases what really happens.