There are seven adult khrast in this one place at this one time; this doesn't say much about how many there are in general. Remember, Hesseth herself has just come back from the human lands; she's in all likelihood not from this particular place.

I would understand the statement to say that the several families are among all the rakh, in the various regions, or at least among a larger community, not just in this one place. But yeah, there's probably some weeding out going on as well.