When I was a little kid, this was my most favorite movie EVER. I loved it. I still have the VHS tape of it. (My parents taped it for me off of Showtime, I think.) Anyway, my tape is in horrible shape, and I have searched for it for years. Well, someone finally uploaded it to YouTube!!! It is cheesy and very late 70s/early 80s...but it is just something bizarre from my childhood. Watching it was such an imaginative experience for me, for some reason. The best part of this movie is just that there really is no resolution. And it is just downright creepy. The girl who plays the older sister (Judith) is great at creating mystery. Here is Part 1...
Oh, CRAZY!! Here is a homemade trailer for my other favorite movie as a kid: the movie version of Anna to the Infinite Power!! It was also so creepy and about cloning!! Again: super cheese. But I loved it.
Both of these movies are based on books:
Phyllis Reynolds Naylor's Witch's Sister and Mildred Ames's Anna to the Infinite Power (which I think is out of print now...but you can find it used, and I found one at my local library book sale years ago).