Evil Stalks This House (1981)

Jack Palance stars as a self-serving, abusive boor who becomes stranded (along with his two children) by a thunderstorm, forcing them to take shelter in an isolated country estate owned by a group of mysterious and wealthy old dowagers. Seeing a golden opportunity, Palance soon turns to plundering their estate, but his plans collide with the secret activities of a Satanic snake-cult who carry out ritual sacrifices in the attic.