I looked up on Disney Wiki for the lyrics to song Hellfire. It said that the choir sang "Mea maxima cupla" two times, but I only heard it once. Am I deaf and someone else heard them sing it two times?

I don't know. It could be a low echoing sound of them saying it the 2nd time. It's been awhile since I listened to the song. I might need to go check it out on Youtube sometime to see. When I do I'll come but with a better answer if I hear them saying it twice or not.