Call it a case of growing pains... or sibling rivalry. I can't help but wonder what exactly is going on at ABC's Brothers & Sisters , the freshman drama starring Calista Flockhart, Rachel Griffiths, Balthazar Getty, Dave Annabel, and Sally Field as the only-on-TV-are-these-people-related Walker family of not so sunny California. (Ron Rifkin and Patricia Wettig also star.) When the behind-the-scenes drama on a series seems more intense than the actual show itself, that's a sign for alarm, especially as fall premiere dates seem to be looming ever closer. First, there were the well-publicized cast changes . Jonathan LaPaglia and Betty Buckley were voted off the island; replacing them are Matthew Rhys and Sally Field. Okay, post-pilot cast changes/additions are always to be expected and nine times out of ten they're really for the best. (Just look at the original Willow on the pilot presentation of Buffy the Vampire Slayer if you don't believe me.) News leaked out