The values in your table seem right. The formula for population is very simple:
population = number_of_buildings * random_number_around( 5 )
Why?
- The average number of persons per household was much higher in a medieval rural settlement than in a modern city. The household usually consisted of an extended family (as @SophieNicole mentioned): the main couple, their children (not 1-2, but rather 3-4), some of their unmarried brothers and sisters, the husband's parents etc.
- I use a much smaller multiplier (5) than a reasonable average number of persons per household to take into account the fact not all buildings are farmhouses. Another reason is to make that value not so odd for a modern eye.
- I use random numbers instead of a fixed value to disguise the simplicity of the formula (otherwise the population of a hamlet of two houses would always be 10 for example) and also to "emulate" cultural differences.