Can co-authors disagree in their own paper?
It is rather unusual, but it has occurred before. In the paper


  Piccione, Michele, and Ariel Rubinstein. "Equilibrium in the Jungle." The Economic Journal 117.522 (2007): 883-896.


each of the authors has their own conclusions, marked "4.1. Concluding Comments by MP" and "4.2. Concluding Comments by AR." It should be noted though that the writing in economics tends to be less structured (no such thing as a "method section") and this is a somewhat unconventional paper to begin with.