added the public key used to login the first vm to the second vm .ssh/authorized_keys:
c2 = Connection(sshB, user=userB, gateway=c1)
copy the key used to login the second VM to the local host:
c2 = Connection(sshB, user=userB, connect_kwargs={"key_filename":path_to_the_private_file,'passphrase': pass}, gateway=c1)
there are two solutions:
c2 = Connection(sshB, user=userB, gateway=c1)
c2 = Connection(sshB, user=userB, connect_kwargs={"key_filename":path_to_the_private_file,'passphrase': pass}, gateway=c1)