Dislocation-mediated plasticity in perovskite oxides depends strongly on chemistry, yet why chemically similar compounds can be either plastically deformable or brittle remains poorly understood. In this work, we apply a phase-field dislocation dynamics (PFDD) framework informed by ab initio γ-surface calculations to study dislocation core structure and glide resistance in four cubic perovskite oxides: SrTiO₃, CaTiO₃, KNbO₃, and KTaO₃. In all four, full 〈110〉 dislocations dissociate into collinear ½〈110〉 partials separated by an antiphase boundary, with separation distances that agree well with experimental and atomistic benchmarks. The potassium-containing perovskites have much wider dissociated cores, consistent with their lower antiphase boundary energies. Peierls stress calculations show that CaTiO₃ has the highest lattice resistance and SrTiO₃ the lowest, matching the experimentally observed ranking of plastic deformability. We also find a two-stage glide mechanism in KNbO₃ and KTaO₃, in which the leading and trailing partials depin at different stresses. These results show that PFDD offers an efficient, transferable way to link ab initio fault energetics to dislocation dynamics across complex oxide chemistries.