As soon as a character refers to their sibling as that "big bro, sis" it is a big sign that the writing is poor. And unbelievable. To me the major failure was they were trying to deal with several story lines; that on their own would have been interesting, but all together it is just messy and highly unrealistic and leaves more questions than answers.
It's a great cast and they really try to sell what has been written without rolling their eyes. It just does not quite get there. ever.