This movie made no sense at all! *spoiler*

1. Yes, the baby is Sam (the teenage girl)
2. The husband is the evil drunken dad aka Sam's mother's partner

3. The evil is the spirit of the woman that the female doctor's husband (the guy that gets killed in the beginning of the movie) was having an affair with. You see her bringing the baby to the Morello house in the flashback.

4. The female doctor was not possessed. The female doctor was most likely feeling jealous and furious because of her husband having an affair with the woman. The spirit only came into being when she was tortured/murdered by the angry female doctor.

5. The boyfriend was likely killed by Sam and/or Sam's ghost mother because he boarded up the room and burned the box according to the 'advice' of the female doctor, thus destroying the evidence of the female doctor's evil deeds (i.e. Sam's mother's murder).

Sam is the baby in the flashbacks. Her mother was married (to the drunk) but had an affair with the doctors husband and had Sam. He helped his wife, the doctor, cover up the murder and he was the one who put his hand over their son's mouth telling him to stay quiet/still. I am guessing the family lived in complete fear of the doctor which is why the husband and son obeyed.

Sam lives with her mother's husband (who she cheated on). He does say she "is a whore just like her mother". They believe the mother ran off with someone when Sam was a baby. But she was killed by the doctor out of jealousy.

The part I don't get is why Sam repeatedly says she had been in the house before. Is it because she was there when she was a baby? Obviously the doctor's children died when she was young so she wasn't friends with them. That's what I didn't get.

Uh no, the husband was killed in the beginning of the film - did you not pay attention? Her mom cheated on Sam's dad with the doctor's husband, who died in the beginning of the film.