This book is probably from the 70s or early 80s. A girl's mother dies, and she and her father go to live in another town with her mother's relatives. The town looks relatively normal at first, but the town doesn't seem to have any contact with the outside world.
Eventually she figures out the people are aliens and they've been repairing their space ship to go back to wherever they came from, and she is helped by an alien boy to escape. The aliens look human except they have a sort of jelly-like substance covering over their eyes. After she escapes she goes to her aunt's house, who she discovers has jelly-covered eyes.