The rapid proliferation of IoT devices has introduced complex challenges in access control particularly due to the limited capabilities of smart objects. This is further complicated when devices from different organizations must collaborate securely and efficiently. To address these challenges, we present a novel approach that combines blockchain technology with Virtual Private Network (VPN) systems to optimize access control in inter-organizational IoT networks. Our solution ensures secure, real-time responses with scalability and lightweight performance by aggregating devices into a shared VPN and enforcing access through decentralized blockchain mechanisms. For better VPN management efficiency, we propose a distributed VPN architecture using fog computing nodes and the DHT-based Chord protocol to overcome the limitations of traditional VPNs, such as single-point of failure. To ensure dynamic adaptability, we extend our work by introducing a hybrid reputation-based Intrusion Detection System (IDS). This IDS continuously monitors and evaluates the behavior of IoT devices, leveraging reputation scores to detect anomalies, and respond to evolving threats in real-time.