Well, Disney's Princess Anne isn't in Genovia anymore... Anne Hathaway ("Princess Diaries," "Becoming Jane" and "Get Smart") is Kym, who getting a temporary pass from her current stint in rehab so she can attend her sister Rachel's wedding. She is a self-centered, emotionally starved whack job with little or no regard for the rest of her dysfunctional family.
Her long-suffering sister, the eponymous Rachel, is played by Rosemarie DeWitt ("Off the Black" and "Cinderella Man"). In my opinion, it will be the quality of DeWitt's performance that will elevate Hathaway's to possible Oscar contention, in much the same way that Daniel Day Lewis owes his statue to Paul Dano who collaborated with him in those extended, Oscar-worthy scenes in "There Will Be Blood."
The brilliant Bill Irwin ("Across the Universe," lots of "Sesame Street" on television and a 2005 Tony for "Who's Afraid of Virginia Woolf?") plays their divorced and happily remarried father, limited by the script to being concerned, perplexed and consistently loving.
Anna Deavere Smith ("The Manchurian Candidate" - 2004, and "Rent" but better known to me as a playwright) has a largely non-verbal role as the girls' stepmother.
Debra Winger, a Hollywood favorite, primarily because she is so reclusive and eccentric, makes a quiet but ultimately explosive appearance as the sisters' mother. We all remember her from those early classics "An Officer and a Gentleman" and "Terms of Endearment," but she has been working steadily ("Big Bad Love" and "Radio").
This is NOT a fun movie. The extra-long scenes that hammered home their point about multi-generational and multi-cultural harmony, ultimately became wearisome. In my opinion, our unhappy Kym had some legitimate gripes and may never see the end of her misery. Her parents will go on living their separate lives and never "get" the overwrought relationship between their two daughters.