The answer to a lot of those questions depends on how the device is programmed. A computer capable of driving around and recognizing where the road goes is likely to have the ability to visually distinguish a human from an animal, whether that be based on outline, image, or size. With sufficiently sharp image recognition, it might be able to count the number and kind of people in another vehicle. It could even use existing data on the likelihood of injury to people in different kinds of vehicles.
Ultimately, people disagree on the ethical choices involved. Perhaps there could be "ethics settings" for the user/owner to configure, like "consider life count only" vs. "younger lives are more valuable." I personally would think it's not terribly controversial that a machine should damage itself before harming a human, but people disagree on how important pet lives are. If explicit kill-this-first settings would make people uneasy, the answers could be determined from a questionnaire given to the user.
