RATIONALE: Giving chemotherapy drugs, such as busulfan, melphalan, and thiotepa, before a donor stem cell transplant helps stop the growth of tumor cells and prepares the patient's bone marrow for the stem cells. When the healthy stem cells from a donor are infused into the patient they may help the patient's bone marrow make stem cells, red blood cells, white blood cells, and platelets. Sometimes the transplanted cells from a donor can make an immune response against the body's normal tissues. Giving tacrolimus, sirolimus, and mycophenolate mofetil may stop this from happening. PURPOSE: This phase II trial is studying how well giving busulfan together with melphalan and thiotepa followed by a donor stem cell transplant works in treating patients with high-risk Ewing's tumors.

OBJECTIVES: * Evaluate disease-free and overall survival of patients with high-risk tumors of the Ewing's family treated with unmodified T-cell depleted allogeneic hematopoietic stem cell transplantation after cytoreduction comprising busulfan, melphalan, and thiotepa. * Determine the regimen-related morbidity and mortality in these patients. * Determine the incidence of acute and chronic graft-vs-host disease in patients treated with this regimen. * Determine the biologic response of minimal residual disease in patients treated with this regimen. OUTLINE: This is a prospective study. * Myeloablative preparative regimen: Patients receive busulfan IV over 2 hours every 6 hours on days -8 to -6, melphalan IV over 20 minutes on days -5 to -3, and thiotepa IV over 4 hours on day -2. * Allogeneic hematopoietic stem cell transplant: Patients undergo allogeneic bone marrow or T-cell depleted peripheral blood stem cell transplantation on day 0. * Graft-vs-host disease (GVHD) prophylaxis: Patients receive treatment according to institutional guidelines and are given treatment against infection. After completion of study treatment, patients are followed periodically for at least 3 years.