Bravo, this is a nice analysis.

I think you should carry through the experiments you suggest. I'm assuming you don't want to actually kill your brother, so perhaps you could gather some test subjects, ask them to imagine being in the situations listed, and ask them to report the magnitude of their hypothetical guilt. Imperfect, but I think this kind of experiment is fairly widely accepted in the relevant journals. Then publish in a top evo-psych journal.