The incredible bad TV cast includes Richard Crenna (dad), Yvette Mimieux (mom), and Kim Richards and Ike Eisenmann (brother and sister). Richards and Eisenmann also starred as siblings in Disney’s Escape to Witch Mountain (1975) and Return from Witch Mountain (1978). (My first two crushes were Richards and Maria Persson, who played Annika in the Pippi Longstocking movies.)
As of now, you can watch Devil Dog: The Hound of Hell here. Skip to the 1:28:20 mark to see the final encounter between Crenna and the devil dog in its wretchedly rendered demonic state. Rawr!
2 Warps to Neptune 
Hammer regular Martine Beswick as well playing the evil woman part.