The Unseen (1980)

Freelance reporter Jennifer and her two friends Karen and Vicki accept an invitation for cheap room and board in a large farmhouse offered by friendly but shady museum owner Ernest Keller, since all the motels in and around town are booked for a holiday parade and fair which Jennifer is covering.

But unknown to the women, some unseen "thing" has been living in the basement of the house for over 20 years and is looked after by Keller and his shy sister Virginia, and it gets out and starts harassing and killing the women, one by one, in violent but seemingly-accidental means.