  The hyperfine structure of the ground states in a number of positronium
hydrides (TPs, DPs, ${}^{1}$HPs) and MuPs ($\mu^{+} e^{-}_2 e^{+}$) is
determined with the use of highly accurate variational wave functions. We also
evaluate the probabilities of various processes in the MuPs system, including
the $(e^{-}, e^{+})$-pair annihilation and its conversion into the charge
conjugate system $\mu^{+} e^{-}_2 e^{+} \to \mu^{-} e^{-} e^{+}_2$.
