Digital twins are a concept that has initially become popular in an industrial context to support product life cycle management. Over time, the number of domains where this concept is applied has grown significantly. This includes, in particular, domains where distributed digital infrastructures become mandatory for operating digital twins. A prominent example is the earth systems, weather, and climate domain. In the area of digital infrastructures, we observe significant efforts towards the federation of computing, storage, and data management services. In the context of digital twins, we consider efforts of particular interest that aim for distributed digital infrastructures based on geographically distributed resources with services operated by a diversity of organisations. In this paper, we review a selection of use cases for distributed digital twins. Analysing these use cases and their implementation leads us to a set of common features and requirements. The key idea of this paper is to link these to earlier identified research and development challenges in the area of federated digital infrastructures.