I remember this film about two kids (or maybe just a boy) living with their grandparents and constantly being scared by this creepy woman with long dark hair who seems to be stalking them

At first it seems like she’s the antagonist but later it’s revealed the children are hers (the product of her father’s rape). I also distinctly remember a scene (maybe the mother’s flashback?) where the father has the dark haired woman tied up and seems to be bleeding her dry.

Any clues??