A software-intensive system-of-systems (SoS) is architecturally designed to exhibit emergent behavior from the interactions between independent constituent systems. With the upcoming generation of connected and automated vehicles, cooperative driving is becoming a major operational domain for safety critical SoS. Overtaking is one of the toughest driving maneuvers for either manual or automated execution, responsible for most of the traffic crashes, e.g., in recent years, almost a third of all people killed on country roads in France died in accidents involving overtaking. This paper investigates a novel approach based on digital twins, where cooperative overtaking is designed to be the emergent behavior outcome of connected and automated vehicles empowered by digital twins, constituting together an SoS. In this approach, each connected and automated vehicle has its own digital twin for cooperative driving, deployed in the cloud, to which it is connected through vehicle-to-network communication. These digital twins, each one influencing the behavior of the corresponding connected and automated vehicle, have their interactions mediated (by design) to raise an emergent behavior resulting in a safe execution of the overtaking maneuver. This novel approach is supported by a model-based engineering workflow and a software toolset for SoS on the Internet-of-Vehicles (IoV).