The saying about family games takes on a disturbing resonance here, though they don't quite reach those depths. “Gregorio” (Martín Adjelmián) and “Mecha” (Graciela Borges) are hosting an unusual collection of relatives at their rundown country house in Argentina. As a storm gathers in the hills, they lounge by a pool that seems like it could harbor piranhas, enjoying wine while their young son and friends play with a…