One error and a couple of things that could be better:
1. Your second sentence should be: How could they sleep so soundly while their fellow prisoner was being tortured in the cruelest way?
2. Cruelest has only one 'L'.
3. The sounds of snoring around the young men were surreal. I prefer: The sound of snoring around the young men was surreal.
Or better yet: The snoring around the young men was surreal. Snoring is, after all, pretty much just a sound, so a little redundant and it's the fact that they were able to sleep that is 'surreal', not actually the sound.
4. I recommend you change the last sentence to: How can human beings adapt to hell so quickly? Using the present tense removes this from the specific (past) situation and expands it to include all times and situations, making it a 'bigger' question.
Student or Learner