In the context of Real Estate Management, Digital Twins (DTs) can act as transformative tools for the integration of sustainability into construction practices by providing dynamic, data-driven virtual representations of physical assets. They enable stakeholders to optimise processes, reduce resource consumption, and align with sustainability objectives. However, effective implementation of DTs, in this context, remains limited by fragmented data ecosystems across different organisations, incomplete integration with regulatory frameworks, and insufficient consideration of sustainability goals. This is especially challenging, as access to high quality, and integrated, data is critical for DTs. Enterprise Architecture (EA) is generally used as an instrument to aid in managing and coordinating such challenges, as it provides a structured approach to addressing these challenges by aligning technical, organisational, and sustainability objectives. In line with this, we propose three primary research objectives: (1) assessing the current state of EA approaches for integrating DTs, (2) developing sustainability-oriented EA modelling concepts and design patterns, and (3) exploring the scalability of DTs from individual buildings to smart cities. Our aim is to position DTs as comprehensive decision-support tools for sustainability, enabling stakeholders to achieve better-informed decisions while addressing regulatory compliance, resource efficiency, and life cycle impacts.