To kill Turel you have to wait until he roars and one of the gongs begin
you have to do it fast or you will get shocked. If you hit the gong in
time Turel will lay down for a little bit, you need to get in as many
hits as possible in that time period. Do this a few times and his life
will fall fairly fast.
You practically do the same thing while fighting Janos. You just need to
wait until he does his flying dive at you then run at him swinging. This
battle takes a little longer but he will die eventually. Use the demons
he sends out to your advantage kill them and take their souls you'll
need them to kill Janos he gets hard.