  We derive the complete mixing-demixing phase-diagram relevant to a bosonic
binary mixture confined in a ring trimer and modeled within the Bose-Hubbard
picture. The mixing properties of the two quantum fluids, which are shown to be
strongly affected by the fragmented character of the confining potential, are
evaluated by means of a specific indicator imported from Statistical
Thermodynamics and are shown to depend only on two effective parameters
incorporating the asymmetry between the heteronuclear species. To closely match
realistic experimental conditions, our study is extended also beyond the
pointlike approximation of potential wells by describing the systems in terms
of two coupled Gross-Pitaevskii equations. The resulting mean-field analysis
confirms the rich scenario of mixing-demixing transitions of the mixture and
also constitutes an effective springboard towards a viable experimental
realization. We additionally propose an experimental realization based on a
realistic optical-tweezers system and on mixtures of bosonic $^{23}\mathrm{Na}$
and $^{39}\mathrm{K}$, thanks to the large tunability of their intra- and
inter-species scattering lengths.
