I was under the impression that the 10th son thing was a result of their number system, not really because they made that many suffixes just in case they had 10 sons.
(Seems a lot more effective to name someone suzy'ten than suzy'blah, so when you eventually have suzy'eleven, you're not scrambling for what word to make up for that kid)
If they are normally hitting 1 or 2 kids I would imagine the thing would top out at 5, I mean that would require having at minimum 11 kids. 10 Sons requires at minimum having 21 children. I've been thinking conservatively Keepers have 5 children that can give you around 400 or so per family if you go out to second cousins, so Keeper Enclaves might have something like 1000+
I imagine the excessive females would have an interesting trend in society, perhaps even luring away excess Tia Seeker
I Honestly think that "Due to nature" they would have only 2 or 4 males and the rest would be females. IMO. so if we have a small tribe or group of families, lets say 4 families, with a total of 24 kids, I believe that 1/4 of that would be males and like you said "excessive females would have an interesting trend in society, perhaps even luring away excess Tia Seeker" I think that would be true depending on the tribe, and would a Tia seeker accept the rule of a female if he decides to stay within the families. or it would be a simple one night stand ( knockup "the movie" edition) and goodbye?
It would depend on how extended the family is, I don't imagine its something as simple as nuclear families(mother, father, children) But more extended groupings, allow for signifcantly larger enclaves without becoming full villages or towns.
As for the Tia thing, how actually successful the excess Keeper females are wouldn't matter when they get a reputation for such(They also might get reputations for stealing other races men as well)