Oh I agree that you can tell which is which in several scenes. But I don't think you can decipher much about them.I generally agree with you on that it goes deeper and the Borden twins were characters acting 24/7. However, I slightly disagree on them showing off their true personalities. And props to Christian Bale for this, but if you watch this a number of times, you can tell off which twin is which in virtually every single scene of the film, and it's all because of their personalities, especially when around Sarah. From observance, you know that Albert was the one that was more intelligent as well as more relunctant in going into the extremes that his brother wishes them to go. Fredrick was more callous, more obsessive, and willing to get his hands dirty. But both were prisoners of each other and at times wishes to be free to be themselves, but never could until the night of the hanging (Fredrick representing the dead bird in the cage and Albert being the Prestige at the end).
And actually there are THREE scenes that reveal them as they are. You forgot the carousel scene where Albert asked Fredrick (disguised as Fallon) that Sarah either knows or suspects something and asked to try to do better.
For instance you say that Freddy is callous, but we only observe his callousness when he is playing Borden to Sarah. But he isn't callous. He just isn't the one who loves her. He only appears callous in contrast to his brother for obvious reasons. I think the only real scene where you can call him callous is the dinner scene with Borden/Sarah and Fallon/Olivia. Freddy who is playing Borden is being an a$$hole. But the thing is that he was almost buried to death a few hours before, so you can kind of see his point, lol.
At least that's my opinion.
I think it's because Freddy is the one who displays the most obvious paternal affection for her, both as Fallon and as Borden. It's not conclusive proof like you say, but then again nothing is in this movie.Um, why you say it's obvious that's not Albert's seed? or that Fredrick even f*cked Sarah and vice versa? Not saying that it's unlikely, I think it was highly likely, hence further implied motivation for Sarah to hang herself. But that part is clearly ambiguous. There never was a hint either way, or would they themselves would of known. Sh*t they had trouble knowing which one did the right or incorrect knot for crying out loud, lol.