Miriam never got suspicious that she'd NEVER once seen Emily and Warren in the same room together, even though they were supposedly married? (How did he ever introduce his wife?) And over the years, wouldn't Mariam ever have wondered why her brother Warren (who was born a girl but raised as a boy) was developing breasts--didn't they ever go swimming? (Let's not even get into the issue of her so-called brother starting his menstrual cycle.) Highly entertaining movie but doesn't make a helluva lot of sense.
You didn't pay much attention to the movie, did you?
1. Warren NEVER introduced Emily as his wife, Emily was the only one to say they were married, and that wasn't until the day we saw Mariam come that Emily was trying to kill Helga.
2. Warren's father kept the children separated for a time, trying to toughen Warren up to make a man out of him, so after Warren stole the doll from Mariam, we can guess they didn't see much of each other from there.
3. Warren's parents died when he was still a young child, so Helga took Warren to Denmark, where during that time, they were about the only place performing competent transsexual operations, so Helga put Warren through the procedure to make him a boy instead of a girl, and Warren didn't come back to Miriam until Helga had her stroke.
Good points. But that still doesn't explain why no one (especially Miriam) thought it was strange these two were NEVER seen together EVER--even though they apparently lived in the same house. Or how Warren/Emily could possibly make the quick changes that involved not only changing clothes, wig, mouthpiece, etc. but also applying/removing makeup and, as Warren putting on false eyebrows (Emily's were not thick like Warren's) and a nose prosthetic (the tips of their noses were quite different). And why, after seeing a front-page newspaper sketch of the suspect that looks EXACTLY like Emily, neither the pharmacist or the doctor alert authorities. Or why. . . .
I agree the front page sketch of Emily unrecognized by people is pretty absurd but the other valid points fall into "poetic license" which virtually all thrillers use. Most movies fail the reality test, especially thrillers and action films.