We revisit the sharp-interface continuum thermodynamics of two-phase multicomponent fluid systems, accounting for partial mass and momentum balances both in the bulk phases and on the interface. This allows to describe the transfer of species between the bulk phases and the interface, i.e. ad- and desorption processes. In fact, the transfer of any constituent between the two bulk-phases is considered as a series of ad- and desorption processes. In this framework, all species transfer processes are coupled via the interfacial thermodynamics. As a consequence, the influence of surface active species on the transfer of other constituents can be captured in detail. The derivation of this model class relies on an axiomatic form of the entropy principle which, at the same time, allows for an efficient closure process. This form of the entropy principle has been introduced for one-phase fluid systems in Bothe and Dreyer (2015) as the result of intense joint work of the late Wolfgang Dreyer and the present author.