The first blank has to be consistent with the idea presented in the latter part of the clause: "..seem to denigrate the workers as irresponsible". Only "problematic" fits well.

Now, Let's look at the second blank, the clause: "despite their (ii)___ treatment by the circus seems to make light of the genuine difficulty of their lives". This to me suggests the word has to have a negative connotation because of the information presented like "genuine difficulty of their lives" and "treatment by the circus". So, the word has to be "exploitative", "sympathetic" would change the meaning of the sentence.

The third blank is straightforward. "And yet there is an earthy (iii)___ to their chant-like song, which suggests something admirable about their ability to maintain their spirits despite the conditions under which they live." Yet indicates a shift and the blank should be something that represents "their ability to maintain their spirits", so I would say "vitality" is the best choice, as it means energy or spirit.