Most unrealistic part...
So the kids were Skyping with Mom on a camera that had previously been covered with oven cleaner and was probably not crystal clear. The kid aimed the laptop camera at grandparents. They were on the other side of the back yard. Through a glass window. Mom sees this and instantly tells the kids "Those aren't your grandparents."
She saw a fuzzy image of two old people from across the yard via Skype...and these were people she hadn't even seen in 15 years. And she INSTANTLY knew it?
No way.
At least extend the scene where she says "Kids, I need a closer look."