<Tr> <Th> Nieces </Th> <Td> Elizabeth Walker Olivia Walker Wandell </Td> </Tr> <Tr> <Th> Other relatives </Th> <Td> Robert McCallister Scotty Wandell 3 unnamed half - siblings Ryan Lafferty (stepbrother) </Td> </Tr> <P> Sarah Louise Walker Laurent (formerly Whedon) is a fictional character on the ABC television drama Brothers & Sisters . She is portrayed by actress Rachel Griffiths . </P> <P> Sarah is a member of the Walker Family, but doesn't find out William Walker isn't her biological father until season 5 . A businesswoman in the family business and a mother of two young children, Sarah often struggles to balance her personal life with the duty of being a mother and a wife . Being the oldest of the family, she's very close with all of her half siblings--even though she had trouble working with her brother Tommy at Ojai Foods because of his competitiveness, especially when she was announced in her father's will as the President of Ojai . She was born October 26, 1967 . Nora had thought that Sarah's father was her late husband William Walker until she discovered recently that Sarah's biological father is her former flame Nick Brody . </P>

Who plays sarah walker in brothers and sisters