I watched it at least 15 years ago. There is a nice family, father, mother, kids and also grandparents. This stranger appears in their lives, he looks kind with them, trying to help them with everything. But weird things start to happen, as he causes them troubles but at the same time he provides solutions, in order to gain their trust. I clearly remember the scene where he causes a car accident to the grandparents in their car going off a cliff. I barely remember this family then moves for some days to their house at the mountains for a little break. At the end, he has imprisoned all family’s member except the father, and he perhaps (NOT SURE!) confesses he’s in love with him!!! This actor vaguely looks like Charles Grodin, but I’m 101% sure it’s not him, otherwise I would have found the movie 🙂