The $\ensuremath{\pi}$-nucleus optical potential is extended to open shell nuclei by employing the generalized seniority model and partial Pauli blocking. The calculated optical potentials are fit to $\ensuremath{\pi}$-nucleus elastic scattering data on ${}^{90}\mathrm{Zr}$ and ${}^{208}\mathrm{Pb}$ at resonance as well as low energies. The ranges of the $\ensuremath{\pi}N$ interaction are determined by a best fit to experimental data. The angular distribution at 48 MeV pion lab energy and energy dependence of the double charge exchange cross section on Te isotopes are calculated. The existing experimental data are reproduced by using the ranges in the vicinity of the averaged ranges of ${}^{90}\mathrm{Zr}$ and ${}^{208}\mathrm{Pb}$ determined in fitting elastic-scattering data.