Two of my favorite stories were: "Born to Breed" and "Daddy's Little Babymakers".  IIRC, certain versions implied the main characters were cousins.  I'd love it if someone would combine them into a mega-story.

I've read both stories, long long ago. My impression is that they are basically THE SAME STORY. The formula is exactly the same, there are simply differences in detail: number of offspring, cause of precocious puberty, effects of said cause on various family members. But by and large, they are essentially the same story.

Well if someone wrote them, I'd read it for sure

I think you're right about that. I'm pretty sure they had the same author.