I had a miscarriage because my babies were in the same sac i only pass 1 placenta can i have a healthy baby getting pregnant 4 months time?

Yes: Did the babies die in utero and the labor follows? Even though it was a monochorionic monoamniotic pregnancy (same sac, one placenta), miscarriage of a viable pregnancy is uncommon. This type of pregnancy is at increase risk for intrauterine fetal death not miscarriage at 18 weeks. Usually, Steroids are administered early for fetal lung maturity and delivery by C-section at about 32 weeks.