Other mistake: When Ruby is signing onto America Online to check her mail you hear the dial-up sound before she even clicks on the sign on button.
Other mistake: In the scene where Ruby is writing her parent's lawyer an email, there are no cables connected to the computer she's using, and still she's able to get online. She can't be using an airport, because then you wouldn't get the dialling tone.
Other mistake: When Rhett sees Terry coming up from the car accident that he was in and tells Ruby, she jumps in the front seat of the car. The car is in park, but she moves the lever up, which would mean the car was in the drive position already.
Answer: Terry told them when they first moved in that it was only going to be temporary so that they would think that they would eventually get separate rooms, but I think they always intended to keep Ruby and Rhett together in the same room so that they could easily monitor their movements. The only reason they quickly knocked up a second room (for Ruby) for when the social worker came, was to carry on the charade of being responsible guardians for them, and they knew if the social worker saw that a teenage girl and her younger brother were sharing, it would raise red flags, and they needed everyone to believe that they were responsible enough guardians, so that they could keep the kids and eventually get their hands on the trust.