As for this fic about Ranma knocking up every girl in Nerima.

I don't see it.

Personally, I see all of the girlfriends as a sort of compensation for
a lack of confidence in matters romantic. ("It's Akane's fault that
nothing's happening.  If she wasn't such an unwomanly tomboy...  I mean
just look at all these girls that are chasing me around.  Nothing wrong
with me, no sirre bob!")

But I really haven't seen a single scrap of evidence that there is the
slightest hint of competition in either of their hearts.

My take is that if it wasn't for the engagement holding them back, they
would've already had a traditional "shotgun wedding".