Copepods can be used as fish food but the males of some species can become gill parasites on fish so you have to monitor the fish for this. But they do make good food.
If you post pictures of the other creatures we can try to ID them for you.
Snails should not be kept in live food cultures because some snails are host to parasitic worms that get eaten by daphnia and then fish. Live food cultures should only contain 1 species of organism that is being cultured.
eg: daphnia in green water, or rotifers in green water, or copepods in green water. But do not mix them and get rid of all the snails.