They have 3 vaginas, but the 3 vaginas are inside the cloaca, so there is only one external opening.

The penis is two-pronged to penetrate both lateral vaginas at the same time, though typically only one is fertile at a time. The penis is also inside the cloaca while not erect.

They also have 2 uteri.

The middle vagina is for the baby to leave any of the uteri, and then the baby leaves the body by the cloaca and then gets into the pouch.

https://trishansoz.com/trishansoz/animals/marsupial-reproduction.html