Continuity mistake: When Luke brings Caroline back to the house after knocking her out, Violet demands to know where Ben is. In this shot her tears are black because of the mascara, but in the next shot all her blackened tears have disappeared.
Continuity mistake: When Caroline first arrives at the house for her interview, she closes her car door and it cuts to her reflection walking away from the left hand wing mirror of the car, as if she is walking to the back of the car. The next shot, however, she is walking away from the car door which is directly behind her (rather than the car boot). There is no way she would have been reflected in the wing mirror if she was walking at this angle.
Continuity mistake: When Caroline is on the bus circling the newspaper ad for hospice caretaker, there is a black man, wearing a blue shirt, behind her in the next seat. In the next shot from the outside of the bus, that man in the blue shirt is gone. (On the DVD, there is a short deleted scene of the bus stopping between these two shots, allowing for the man's "disappearance" but it is still a continuity error within the film.)
Continuity mistake: While Caroline gives Ben a bath, she drops the soap into the water causing her to get soap in her eye. When she gets up to check her eye she drops the sponge into the water, but when she returns the sponge is in the bathtub caddy.
Continuity mistake: When Caroline is going to her interview and drives past the older lady and girl on the road, she's wearing the outfit she wore when she moved in, not the interview dress.
Answer: In that particular scene with the servants and the kids, you'll notice that the servants' eyes are rolled back into their heads and they're shaking uncontrollably. I think this is because they were drugged. You'll also notice they never try to fight being hung, never cry out or anything. They just keep shaking with their eyes rolled upward.
They weren't drugged, they were in a possessed state.