After the Line Founder, all families consist of only sons.
Only.
Anything else ends the line.

403 generations...of only sons. After the 33rd generation the changes begin to take hold and the line can be termed Bay Royalist.-34th Bay (67th overall) can choose the sex of their offspring..

EXCEPTION TO THE ONLY SON RULE. After the 66th (33rd generation Bay) a daughter no longer ends the line a daughter is a "line skip link" i.e. the process begins again at the first Bay level- generation 33. This 66th generation is key- "Crisis Generation". In the novel three lines have reached this stage or passed it. Stewert, Mercer and Brekk,

But one line seems dead. The Crisis generation Ven Brekk ended his line by producing twins.. 66th Generation, (33rd Bay) is Crisis generation.

The main character in the novel is another Crisis generation Bay named Teal Ray Stewert. Therefore he must avoid twins or a second son but a daughter will save the line.. As to what happens in the case of 2 daughters or a daughter followed by a son. Well follow the logic above.

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KNOWN CHANGES IN BAYS:
Increased healing powers.. increased endurance, real-time racial memories,,,
New Race
.. mind-reading, empathic powers, water abilities enhanced.