There is also the issue to address of how people think of "the law", on a gut level. Do they think of it as "the law", as an abstract set of rules that are then applied to real life, something outside and identifiable and tangible, or is it simply "the way things are done"? If your group of people is especially small, it might well be the latter, rather than the former, because the momentum of the-way-things-are-always-done carries forwards.
Yes. I think many fantasy authors make a mistake in treating small societies exactly like large ones, so that there's an elaborate trial, with jurors and witnesses and everything, in a village or tribe that only has about fifty people. Frankly, if there are only fifty people, I doubt they could find twelve jurors who are a) adult and b) could spare the time to sit on a jury and deliberate for days. It works out much better with a larger population.