Yakov has a problem that in the movie, Cher ends up with (SPOILER ALERT!) Josh (played by Paul Rudd). He contends that Josh is Cher's brother, whereas he is her former stepbrother, meaning that not only do they not share any blood, there is no formal relationship between the two. Besides, this is based on a Jane Austen novel, and in her books, everyone always ends up marrying their first cousin. This is much better by comparison, right?
Or not. Seriously, I don't know why I'm defending this.