Note that it is only required that children of Genma and Soun marry.
 
 So, the obvious solution is for Genma to adopt Ukyou (fulfilling his
 debt to her) and then Ukyou (legally a boy) marries Akane.
 
 Akane would be much better off (or at least a lot calmer) with a smooth
 talking finacee like Ukyou and she hates boys anyway, right?
 
 Ukyou and Akane!  Ukyou and Akane!

Umm but Soun wants an hier..... who's going to play mommy?
 

 
 Ranma goes back to the village ("I am not a number!") where Cologne
 teaches him some discipline ("Spare the rod, spoil the groom child!").
 Moouse gets Kodachi (she likes getting tied up...), Tatewaki is calmed
 down by Kasumi, Dr Tofu marries the only girl he's ever dated and let's
 see, anybody else?
 
 Oh yeah Ryouga.  Well, he can just get lost.

Hey he could move in with Akane and Ukyou Saotome and father the children!
that'd be scary O_O

 
 Fortunately (for my own health), I'm not writing up any of this. (Except
 maybe Moouse and Kodachi, which would make a strange lemon if nothing
 else.)