Complex sentence: The Gilbreths are now most commonly remembered as the parents of their twelve children, whose upbringing is chronicled in the comic memoir "Cheaper by the Dozen" (1948, very loosely adapted in a 2003 film).
Split into simpler sentences: The Gilbreths are now most commonly remembered as the parents of their twelve children. The upbringing of the twelve Gilbreth children is chronicled in the comic memoir "Cheaper by the Dozen" (1948, very loosely adapted in a 2003 film).