Yep. No more twins after telling CSL not to handle pregnancies.
Still can’t use the framework. Tried a genetics mod which has Big and Small as a dependency and no pawns spawned.
Having noticed some pawns asking to join my colonies being of a xenotype other than what is described, I’ve enabled a mod that recently hit the Workshop.
Going to start a new Red Sun colony to check it out.
One thing I really like about the Red Suns: some piece of their default apparel includes a firefoam grenade launcher. Draft them, line 'em up at a fire, and they’ll have it knocked down in minutes!
Game minutes, that is. 
Thought I would need to rebuild my modlist again when I started getting nothing but black screens upon reaching what should have been the main menu.
Shutting down for a while then rebooting seems to have prompted Steam to update some mods, which fixed whatever was causing that.