So, I've never quite been able to figure this out for 37 years or so. I live in metro Detroit and back in the 1980's they used to show 3 horror movies between 2 local channels on Saturday afternoon. This movie was on during that slot though it seemed more like a thriller.
All I can really remember is the following:
1) Someone is murdering people from a family either for revenge or inheritance
2) It had the look of an Amicus or Hammer period piece (like the Gilded Age)
3) 1st scene that has stuck in my head since: Someone is set on fire in a room with a canopy bed
4) 2nd scene that has stuck with me: The villain (i think) dies in quicksand. Quicksand that looked like oatmeal in water quite frankly, not that it didn't freak me out as a kid.
Hopefully someone has an idea. I was able to figure out my other 2 traumatic childhood movie mysteries: Don't Go to Sleep and Strange Behavior.