The purpose of this study is to identify the recommended Phase 2 regimen(s) (RP2R\[s\]) and schedule for the study treatment (Part 1), to characterize the safety of the RP2R(s) for the study treatment (Part 2) and to evaluate the anticancer activity of talquetamab + teclistamab in participants with relapsed or refractory multiple myeloma and extramedullary disease (EMD) (Part 3).