Second proton and neutron alignments in the doubly-odd nuclei ${}^{154,156}\mathrm{Tb}$

High-spin states in the doubly-odd nuclei ${}^{154,156}\mathrm{Tb}$ have been populated in two separate experiments using the ${}^{36}\mathrm{S}{+}^{124}\mathrm{Sn}$ reaction at different beam energies (160 and 175 MeV). The yrast structures of both nuclei were extended to much higher spin $(I<~48ħ)$ than previously known and several quasiparticle alignments have been identified. These include the second neutron alignment and a clear delineation of the second proton crossing in ${}^{156}\mathrm{Tb}.$ Systematics of these crossings for odd-$Z$ nuclei and comparisons with results of cranked shell model calculations are discussed.