You've one copy of the file, encrypted with N public keys. Each of the corresponding private keys can decrypt the files. Assuming you've all the public keys in

You've one copy of the file, encrypted with N public keys. Each of the corresponding private keys can decrypt the files. Assuming you've all the public keys in your keychain, then for each key you pass "-r <email>" for the encryption, like "gpg -e -r foo@bar.com -r baz@bar.com plain.txt", and for decryption you do something like "gpg --output plain.txt -d plain.txt.gpg".