DONOR: Donors who are not expected to meet the minimum target dose of marrow cells ( x ^ nucleated cells/kg recipient ideal body weight) Subject must have documented monoclonal plasma cells in the bone marrow of ?%, as defined by their institutional standard at some point in their disease history or the presence of a biopsy proven plasmacytoma. Serum M-protein >= g/dl and/or bone marrow plasma cells >= % and < % Participants with platelet level >= ,/mm^, within days of initiation of protocol therapy for patients in whom < % of bone marrow nucleated cells are plasma cells; or platelet count >= ,/mm^ for participants in whom > % of bone marrow nucleated cells are plasma cells; transfusion within days of screening is not allowed to meet platelet eligibility criteria Participants with platelet level < ,/mm^, within days of initiation of protocol therapy for patients in whom < % of bone marrow nucleated cells are plasma cells; or platelet count < ,/mm^ for participants in whom > % of bone marrow nucleated cells are plasma cells; transfusion within days of screening is not allowed to meet platelet eligibility criteria Previous or current diagnosis of symptomatic multiple myeloma, including the presence of lytic bone disease, plasmacytomas, >= percent (%) plasma cells in the bone marrow, or hypercalcemia Monoclonal plasma cells in the bone marrow (BM) % or presence of a biopsy-proven plasmacytoma Additionally, patients must meet criteria for high risk of progression to multiple myeloma by PETHEMA CRITERIA (patients must have at least risk factors present)\r\n* . >= % abnormal plasma cells/total plasma cells in bone marrow compartment (this is measured as a percentage of the total abnormal versus normal plasma cells in the bone marrow compartment using standard flow cytometry of the bone marrow aspirate; having >= % abnormal plasma cells/total plasma cells constitutes a risk factor for progression to multiple myeloma by PETHEMA criteria) \r\n* . Immunoparesis (this term refers to the patient having low uninvolved immunoglobulins in peripheral blood, for example if a patient has IgA smoldering multiple myeloma, then either having a low IgM and/or low IgG will qualify as a risk factor for progression to multiple myeloma)\r\n** of risk factors: high risk for progression at a rate of % at years Bone marrow plasma cells < % or > % Platelet count >= ,/?l (>= ,/?l if bone marrow plasma cells are >= % of cellularity) Clonal bone marrow plasma cells > % Bone marrow plasma cells must make up % or less of total bone marrow cells based on a bone marrow biopsy performed within days of the start of protocol treatment Aggregates or sheets of one of the following: lymphocytes, plasma cells or\n lymphoplasmacytic cells on the bone marrow biopsy (measured within days prior\n to registration). Participants with platelet level < ,/mm^, within days of initiation of protocol therapy for patients in whom < % of bone marrow nucleated cells are plasma cells; or platelet count < ,/mm^ for patients in whom >= % of bone marrow nucleated cells are plasma cells; transfusion within days of screening is not allowed to meet platelet eligibility criteria Platelet count < ,/mm^ within days of initiation of protocol therapy for patients in whom < % of bone marrow nucleated cells are plasma cells; or platelet count < ,/mm^ for patients in whom >= % of bone marrow nucleated cells are plasma cells; transfusion is not allowed to meet platelet eligibility criteria Clonal bone marrow plasma cells ?% or biopsy-proven bony or extramedullary plasmacytoma Platelet count ? X /L (in patients with < % of bone marrow nucleated cells were plasma cells) or ? X /L (in patients with ? % of bone marrow nucleated cells were plasma cells) without transfusion or growth factor support If no monoclonal protein is detected, then ? % monoclonal bone marrow plasma cells Platelets (plt) ? x /L in subjects in whom < % of bone marrow mononuclear cells are plasma cells or ? x /L in subjects in whom ? % of bone marrow mononuclear cells are plasma cells. Platelets inferior to cells per L if inferior to % of bone marrow (BM) nucleated cells are plasma cells, and inferior to cells per L if superior or equal to % of BM nucleated cells are plasma cells. Platelet transfusion is not allowed within three days before the screening visit. Patients with plasma cells > % of bone marrow nucleated cells, and platelets >= ,/uL will be permitted regardless of the baseline ANC, if it is felt to be related to active myeloma and if in the opinion of the investigator, growth factor support can result in improvement in the neutrophil count to greater than /uL (including during screening period) Platelet count >= ,/uL for patients in whom < % of bone marrow nucleated cells are plasma cells; or a platelet count >= ,/uL for patients in whom >= % of bone marrow nucleated cells are plasma cells; platelet transfusions are not allowed within days of last platelet assessment to confirm eligibility Platelet count < ,/ L for patients in whom < % of bone marrow nucleated cells are plasma cells; and < ,/ L for patients in whom ? % of bone marrow nucleated cells are plasma cells Platelet count < x ^/L, unless myeloma-related; if MM-related (hypercellular marrow biopsy of > % and packed with at least % plasma cells) the enrolling investigator must document this Meets criteria for symptomatic multiple myeloma, defined as:\r\n* >= % monoclonal plasma cells in the marrow AND ANY OF THE FOLLOWING:\r\n** Biopsy-confirmed plasmacytoma\r\n** Lytic bone lesion(s)\r\n** Hypercalcemia without other explanation Platelets >= x ^/L; if the bone marrow contains >= % plasma cells, a platelet count of >= x ^/L is allowed Patients must meet the following laboratory criteria within days of starting therapy: * Absolute neutrophil count (ANC) >/= . x ^/L * Hemoglobin >/= g/dl ( transfusion are permitted) * Platelet count > , cells/mm^ for patients with < % of bone marrow plasma cells or platelet count > , cells/mm^ for patients in whom > % of the bone marrow nucleated cells were plasma cells * aspartate aminotransferase (AST) and Alanine aminotransferase (ALT) % lymphoplasmacytic cells or aggregates, sheets, lymphocytes, plasma cells, or lymphoplasmacytic cells on bone marrow biopsy; quantitative immunoglobulin (Ig)M monoclonal protein > , mg/dL DONOR: Donors who are not expected to meet the minimum target dose of marrow cells ( x ^ nucleated cells/kg recipient ideal body weight [IBW]) for the initial HCT; the average nucleated cell content of harvested marrow is x ^ nucleated cells/mL or x ^ nucleated cells/Liter Platelet count > , cells/mm^ for patients with < % of bone marrow plasma cells OR platelet count > , cells/mm^ for patients in whom > % of the bone marrow nucleated cells were plasma cells Bone marrow plasma cells ? % or clinical manifestations of multiple myeloma, such as hypercalcemia or lytic bone lesions Absolute neutrophil count (ANC) >= . x ^/L for patients in whom < % of bone marrow nucleated cells are plasma cells; or an ANC > . x ^/L for patients in whom > % of bone marrow nucleated cells are plasma cells; ANC must be independent of granulocyte colony-stimulating factor (G-CSF) for >= week and pegylated G-CSF for >= weeks prior to screening Platelets >= x ^/L for patients in whom < % of bone marrow nucleated cells are plasma cells; or > x ^/L for patients in whom > % of bone marrow nucleated cells are plasma cells; screening platelet count independent of platelet transfusions for at least weeks Platelet count of ? x/L in patients in whom <% of bone marrow nucleated cells are plasma cells and ?x/L in patients in whom more than % of bone marrow nucleated cells are plasma cells. Platelet count < ,/ ?L for subjects in whom < % of bone marrow nucleated cells are plasma cells Monoclonal plasma cells in the bone marrow ?% and/or presence of a biopsy-proven plasmacytoma Monoclonal plasma cells in the bone marrow greater than or equal to % and/or presence of a biopsy-proven plasmacytoma, and