I don't make a conscious choice to take action that will cause a stranger's death (even if more people die because I didn't take action) with exceptions for my monkeysphere. In the case of the worst enemy one, I didn't hesitate to run them over. In the case of self preservation, I chose to save myself. In the case of my best friend, other people are gonna die. Etc.

It makes a lot of these pretty easy and a few (like first cousin vs 3rd cousins) a matter of happenstance, just like the happenstance that I was looking at these absurd trolley problems.