Is this movie set during the same time as Maximum Overdrive? Because that could explain some of the goings on. We can blame Catherine for the fish, the tiles, the pills and some of the other machine free murders, but the machine malfunctions could be the Maximum Overdrive effect (including the screws which are simple machines).
Also, at one point in the film, it is said that Catherine went mad after the birth accident. Understandable, but maybe the reason she killed herself so violently was because the spirit of the miscarried child was haunting her in the same way that she was haunting Michael. In the end the baby and Catherine just wanted to be a happy family living together in Hell with Michael.