I think I can finally stump ...
Question: I think I can finally stump you: I remember an old horror movie where an older couple takes control of a younger couple. They make them do as they please and experience what the young people do. One scene I remember in particular is when they do a "test" and make one of them crush an egg in his/her hand. Naturally, these things end badly. Does this sound familiar?
Answer: Very. You saw The Sorcerers (1967), with Boris Karloff as a scientist who develops a device that lets people control others and vicariously enjoy their experiences, and veteran British actress Catherine Lacey as his wife. Karloff tests the device on a young man, but his wife gets hooked on the process and forces him to commit increasingly sadistic acts for her entertainment. As you say, it all ends badly. The Sorcerers is one of only three films directed by promising English filmmaker Michael Reeves, who died at the age of 24 after completing the remarkable Witchfinder General/The Conqueror Worm (1968).