Borden and Fallon question

They never used the machine. They were actual twins.

Let's be bad guys.

I'm going to wager that the twins started their "trick" when they started in the business. Stage magician is of course not a career newbies get to be the front stage attraction. So they probably agreed to enter the local/wherever magic scene with the Alfred identity with the brothers alternating nights. Realistically not that hard to keep that under wraps. Along as the one stays hidden and the one that went in reports everything they did/heard/saw.

When he got his own gig as a headliner they added the Fallon identity to travel with the act. Since now there will be more underlings around and there should be a physical engineer(whatever the word is) present so the one brother plays the Fallon role while the other plays Borden.

Then once they got The Transported Man trick up and running it became tradition that they switch then.

That would be my take on how it would make the most sense. Although the whole living the trick all the time, may not have been the brightest idea in the long run, I think that's realistically how'd they pull it off.

Communities left for being too closeminded: Gamefaqs, Home Theater Forum, Toonzone

That's one of the things I loved about the movie is how the secret hid in plain sight from the beginning. When Borden takes Sarah out on their first date and walks her home, he asks to come in for tea. She refuses saying the landlord wouldn't allow it. He turns and leave. Then as she enters the apartment she finds Borden standing there with the teapot.
The audience immediately dismisses this as one of those cute gags that magicians can pull off in movies/tv but would be impossible in real life. But it wasn't that at all....his twin had been waiting in the apartment for her the entire time and it wasn't until watching this again that I realized how clever this bit was.