Yes. Nile monitor lizards, for example, eat the eggs and young of the Nile crocodile, but the adult Nile crocodile may eat the Nile monitor lizard. A bullfrog may eat ducklings, but an adult duck may eat a bullfrog. Young bullfrogs may be eaten by a garter snake or water snake, but an adult bullfrog may feed on a garter snake or water snake.

Yes unless they are an apex predator, which means they are at the top of the food chain. A normal predator can be killed as prey by higher ranked animals.

Alligators.

Humans aren't their primary prey, but they do eat humans.

And we eat them. They are delicious.

Reptiles.

Yes, fish do that all the time.