When Steve is put in the Magic Box in the beginning, through the doorway you can see a patient and a nurse sitting on a bench in the hallway which stretches backwards.
When Mark is running to find the key, the hallway is parallel to the room and the bench is facing the front instead of the side as it was earlier.
It's said that impersonating someone is not a crime. While that is generally true (like someone who works as a celebrity impersonator), it is illegal if the intent is to commit fraud or cover up a crime, both of of which would apply here.
The story ignores the fact that twins, no matter how identical they may be, do not have identical handwriting. It would have been fairly easy to tell them apart.
As a coroner, Amanda should have gotten finger prints from the cadaver (Jeff) as part of the examination. Then, when the question of who is who Steve would have known the fingerprints on the Scotch bottle belonged to those on the cadaver.