It's bugged and fixates on one character and therefore marriage/adoption decisions are next to useless.
Factions which assume this isn't bugged and have the lines matter for 'interloper' etc. are very annoying in this aspect.
Also it really reduces the fun of interesting cultural groups and associated traits that obviously a lot of effort went into because you have next to no control over it and the game pretends you do.
Short of being able to fix this bug which presumably isn't possible, does anyone have any ideas on if the following workarounds can be achieved?
1. A console command to simply delete characters. This would avoid having to load non-royals up on a leaky canoe and sailing them into the nearest Spanish Armada.
2. A setting to change (lower) the chances of female children or simply remove them and have another mechanism for introduction of new lines.
3. A way to change the cultural group of a character in-game (probably not doable)
4. Any other ideas?
At the moment I'm simply refusing all marriages and adoptions which is very unfun. Will try setting the "past child-bearing age" for females to 17 next game I guess, but will probably just play a faction where the lines don't matter instead.