My twin babies died in me for 3 weeks and i gave birth,they were in the same sac and i pass only 1 placenta,is it ok to get pregnant 4 months after?

Yes: Four months is long enough to try to conceive again. Good Luck for a healthy successful pregnancy this time. :)

Monoamnionic twins: Of all "identical" twins, the rarest and most dangerous of all have monoamnionic monochorionic placentation, meaning one amnionic sac contains both, nourished from a single placenta, detectible by 9-10 weeks. These twins hardly ever survive because no membrane separates their cords, so normal movement will eventually wind up twisting the two cords around each other until strangulation occurs.