[quote="SillydogTheGreat"]Actually Nala is of royal blood. Mufasa being the only male in the pride is able to mate with all the females. I do believe that Mufasa is Nala's father as well, making her Simba's half-sister and making her an obvious choice to be betrothed to him.[/quote]
Nala is not of royal blood, and isn't Mufasa's daughter.

Mufasa never acknowledged Nala as her daughter not one time in the movie. Also, if she was Mufasa's daughter, Scar would've killed her to usurp the throne because Nala would be Mufasa's blood heir to the throne same as Simba. But, the movie never mentions this, thus Nala is not Mufasa's daughter nor is Simba's half-sister.
[quote="SillydogTheGreat"]Even if you don't believe the theory of Mufasa being Nala's father, there is still the other theory that Sarafina and Sarabi were sisters. We know for a fact that Sarabi's parents were royalty, and if Sarafina was her sister it makes her royal by default as well.[/quote]
Quit oozing your fan theories as facts. When during the movie, did it state Sarabi's parents were of royalty? Sarabi is only mufasa's queen consort, because she was obviously bethrothed to Mufasa.