Who ever adopts without running it by the biological kids first?!!!
Seriously.
According to the film, the kids were never even asked whether they wanted an adopted sibling.
It's one thing to give birth to a new family member (you don't need to run that one past the kids), but quite another to adopt a freaking grown kid (9 years old) who's a total stranger and the kids will have to interact and deal with form now on.
Doesn't anyone think they deserve a say, or at least MEET the possible new addition to see if they actually get along before adopting the new kid?!!!!
I mean, divorcees or single moms with kids do precisely that (making sure their kids get along) before considering marring other people with kids of their own.