This topic never dies.
I see the same arguments all over again for many years already
And i do have an answer, which is course only my opinoin, you are free to disagree with it, but i highly doubt you could dissuade me.
1) BBC, Kenya, Serengheti. You should never preject these or any other such sources of information into TLK universe intact. Social structure of TLK pride is far from what you can see in wildlife, it is closer to human medieval standrarts. Why, would you ask? Because if it was a "real lions" pride, then Scar would not exist. Mufasa would just kick him out or kill, rather than suffer his poisonous annoying presence only because Mufasa is a "good guy" and the baddie is his brother. Also real lions do not care about "ruling a kingdom" along many other things. No. TLK lions are much more like humans in lion skins, see them like that and you wont be mistaken.
2) It's either Mufasa or Scar? Nope, wrong again. As Simba told in the movie - "she is my
friend", don't you think if it was Muf or scar, that would be "my
sister"? Of course sisters can be friends and not-much-friends, but nobody calls a sister "friend", ever, period. I have a sister myself, some times we were good friends, especially in early childhood, i was always calling her "sister". Friends or not, she is still a family, family blood, friendship come and leave but family bounds remain, that's why you call them "bro", "sis", "dad", "mom"..
3) So what's up, there is no other lions! Nope, wrong again. Muf's pride actually had quite a bunch of other cubs and even adult-adolescent lions, as you can see in TLK 6 new adventures and other support
disney media. So, this point is not valid. So, they were not shown in the film but they actually meant to exist according to disney itself. Case closed.
4) So, it was some outstage pridelander, eh? Perhaps, but i think nope again. Because i see how different Nala and Sarafina are from other lionesses of the pride. Why is that?
5) Here we come to possible answers. And they all would be nothing but speculation and fantasies. Let me share my own version - Sarafina came to Myfasa's pride from elsewhere, already being pregnant, and got adopted by pridelanders. What happened to her original pride or what a twist of fate caused that journey, who would know..