No parent=
 in their right mind would name a child  Ranma' or  Ryouga' or even 
Nabiki' 
<<<<<<<<<<<<<<<

Well, I don't know about Ryouga's parents, but it could be argued that
Gemna and Nodoka aren't in their right minds (Genma we all know too
well.  As for Nodoka, well, besides the whole seppuku thing, she married
Genma.  Ranma himself is surprised when he finally 'meets' his mother)