I have reached the following conclusions based on the poll and other input.
1. I'm accepting Lalato's proposal that the Kelvin family is descended from the indigenous sheep herder culture.
2. I'm going with the idea that the Kelvin family has ruled the city since the days of the founding.
3. I'm going with the idea that the majority of the ruling Kelvins have been female.
4. I'm going with the idea that the succession process is that the ruler appoints his/her successor from amongst the eligible members of the Kelvin clan.
Thanks everyone for your input.
The revised historical synthesis is now available on the History thread.