Amnion is the membrane that covers the embryo. Chorion is the membrane that covers the amnion, the yolk sac, and the allantois. The space delimited by the chorion and the amnion is called amniotic...
No. Two placentas indicates dizygotic twins which always has 2 amnions and 2 chorions.This is a common misconception. My own twins are identical, yet they had separate sacs and separate placentas...