Book about a family of teenagers who kill living people to stay alive forever

Question

I read it as a teenager, probably late 80s early 90s. In it there is a family of beautiful, mysterious teenagers who captivate everyone in school/town. It turns out in the end that they are a race of ancient dinosaurs who kill living people to stay alive forever. The only other detail I can recall is that there is a handicapped boy that the mean to throw over the cliff as a sacrifice, but someone snaps his neck so that they won't get power from the death.

Answer 1

Nine years later but... this is surely Christopher Pike's Scavenger Hunt (1989). The setup is the same and the end reveal - that they're actually dinosaurs disguised as people - is, in fact, a thing.

Back of the book:

School was almost over. A secretive club on campus had organized a scavenger hunt for the entire senior class. In small groups, and with the help of cleverly planted clues, the kids are led throughout the city, and then deep into a night-time desert. The sponsoring club has promised a wonderful prize for the first group to reach the goal of the hunt. But for Carl Timmons, a troubled young man who has recently lost his best friend, the hunt will become a nightmare. Led astray by his love for a strangely beautiful girl, he will wander far from the others, and back into a haunted past, where the line between the living and the dead is blurred and broken.

And the dino twist per Oh God Why?'s review:

Rick again asks Davey to tell him about the people who built this place, and Davey tells him they were very old, and of a different order. And not people as you know them. Oh, and they were hundreds of millions of years old. Rick starts to say that’s impossible, man hasn’t been on this planet that long, but Davey interrupts him to scoff that man is nothing, man is a soft-skinned freak who will have his day and then be gone! They ruled this planet for millions of years, and they’ll rule it again!

The kids are like, uh what? ... He explains that Davey is implying that an intelligent race evolved from dinosaurs and formed a civilization.

I’m not sure why ancient dinosaur people want to go to high school, but fine, I guess. That would be the last f**ing thing I would want to do.

And again, on Young Adult Revisited's review:

Carl’s group finds another box, which has a bloody and ripped shirt inside, which Tom points on. When they reach the cave, they send Tom away and make Carl start digging. Tracie’s group shows up to meet them and she reveals that they know the secret. Cessy kind of steps back and ignores everyone, while Davey takes control. He starts talking about a group of reptilian creatures that evolved beyond the dinosaurs.