Driven by the global energy transition, the European Commission has introduced Renewable and Local Energy Communities (LECs) to empower citizens, stimulate local investment, and unlock flexibility within electricity systems. As these frameworks mature, the scope of LECs is expanding beyond simple electricity sharing to encompass multiple energy vectors, including heating, cooling, and electric mobility. This PhD research, supported by the EFES project (Win4Excellence), proposes a comprehensive study of internal market design for these evolving multi-sector communities, with a particular focus on the integration of the electricity and mobility sectors. The research investigates the flexibility potential associated with the ongoing paradigm shift from internal combustion vehicles to electric mobility. In particular, it analyzes how electric vehicles and related charging infrastructures can act as flexible assets within local energy systems. The study also examines the impacts of this integration on low-voltage distribution networks, highlighting both the operational challenges and the opportunities that electric mobility may create. Ultimately, this thesis aims to develop a scalable framework enabling multi-sector LECs to operate efficiently and fairly, positioning them as valuable building blocks of the future decentralized energy landscape.