My sister in law is pregnant, dilating at six months, having twins, what is the risk?can they survive? shes only 21

That's too early...: Baby fetuses should stay inside the mom as long as possible (as long as it's safe for the babies). Six months is about 26 weeks, depending on who's counting, and is still too early to be born. Nowadays, survival rates are not bad at 26 weeks, but mere survival is not the goal. The goal is a happy baby with a normal brain and a normal body.