When the Griffin family enters the Space Shuttle, the floor and seats are level with the horizon - in other words, as it would be after it landed. The Shuttle however is in launch position which means they would have to be climbing everywhere.
If you huck an egg in zero gravity, it will fly just as fast as on Earth (faster if anything.) The reason objects are floating slowly in videos from the International Space Station and such is that everybody carefully avoids throwing them at high speed in the first place.
The Space Shuttle brake chutes are not mounted in the middle of the vertical stabilizer but at its root.