“Inconceivable” (** out of four) a well-made but obvious, empty melodrama about a couple (Nicholas Cage and Gina Gershon) unable to have kids of their own who turn to a friendly new neighbor (Nicky Whelan) to be their surrogate mom but they soon grow suspicious of her and realize she may not be who she says. What’s really inconceivable is so many good actors were attracted to this mediocrity. Competent direction can’t enrich routine story and script, which is predictable at every turn. Faye Dunaway is wasted in a supporting role as Cage’s mom; Cage and Gershon first starred in the much more electric “Face/Off” 20 years earlier.