The Visit(2015)

Tyler (Ed Oxenbould) and Becca (Olivia DeJonge) go to spend the week with their estranged grandparents while their mom is on vacation with her new boyfriend. Little do they know, but the grandparents are actually patients at a mental hospital, who killed the real grandparents and took over their lives when they heard of the upcoming visit.

The kids kill the imposters in self-defense, and the mom regrets having a 15-year grudge against her now deceased parents, who were harmless in retrospect.

Becca forgives her father for abandoning the family years ago.