Really? Kids play parents off against each other all the time. Of course the parents should talk privately and then present a united front. That's what seems to be missing here.
I don't see Jazz as anymore of a brat than most 15 year olds. She is spoiled, but far less than many teen-aged girls I know who come from families like hers. And she's the baby of the family, which often adds to spoiling. (just ask my 55-year old "baby" brother . . . still spoiled!)
And she has always had special needs. I do feel for the other children, but I have a feeling their "resentment" is being played up for the show. Overall, they all seem to have good relationships with each other and their parents.