Four Christmases (2008)

Brad and Kate have been together three years, in love, having fun, doing all sorts of things together with no intention of marriage or children. Christmas morning, they're on their way to Fiji, having told their two sets of divorced parents that they're off to do charity work. Through a fluke, they have no choice but to visit each of their four idiosyncratic parents. As the day progresses, Brad and Kate remember growing up, each learns more about the other, and Kate realizes that her life may not be as good as it could be. Do they know each other well enough to weather the storms families bring?