In many complex oxide thin films, a combination of local (, defects or chemical inhomogeneity) and film-scale (, composition or boundary constraints) factors can induce unique or emergent properties, requiring high-resolution characterization to fully understand them. Here, we combine aberration-corrected scanning transmission electron microscopy and multislice electron ptychography to characterize thin films of the multiferroic (1-)-(). Nano-beam electron diffraction and atomic-resolution imaging first reveal a composition-dependent structural evolution from rhombohedral-like monoclinic to tetragonal symmetry, characterized by increased structural disorder as content increases. Further, antisite defects are found to introduce local fluctuations in polarization. Using depth-resolved multislice electron ptychography, the antisites are shown to form two-dimensional clusters that lie perpendicular to the growth direction and are surrounded by significant lattice distortions. Enabled by the depth resolution of multislice ptychography, the average three-dimensional structure surrounding the antisite clusters is extracted to form defect motifs. In films with higher content, the magnitude of antisite-induced distortions is diminished and correlated with the increase in film tetragonality. These results demonstrate that structural analysis of a functional oxide using a complementary combination of conventional imaging and ptychography can provide direct 3D visualization of defects and their associated distortions, thereby decoupling their effects from overall composition-induced structural changes.