Hi! Nice to hear from you! I like what you've written in your journal, and I think I have a few things to add:

Ni not only has much less mane than Kovu, but he is much smaller. Kovu is about 3/4ths as big as Simba, while Ni is only about twice as big as cub Nala. Also, Ni's toe color isn't the same color as his pelt: it's just the tiniest degree lighter (the same color as his muzzle and belly).

I like the "Tojo is Vitani's father" and "Chumvi is Kovu's father" theories, but I personally like to think of the two having the same father, just for simplicity's sake. The two have traits so different than Zira's that it might be easier to suppose that their real parents were Tojo (blue eyes, tan fur, ear rims) and Kula (dark fur), but if Zira has to be their real mother and they share the same father, either Chumvi and Tojo are brothers (thus sharing the same genes for blue eyes, dark fur, etc.), or Kovu and Vitani got the traits they didn't get from Zira and Chumvi/Tojo from their grandparents (one of Zira's parents could have had dark eye fur and green eyes, one of Chumvi's parents could have had blue eyes and a tan pelt, one of Tojo's parents could have had dark fur).

Another little addition to the Tojo and Tama list: Tojo also has a pink nose. Even though it has the "Pridelander" shape, it seems like Vitani could have gotten the shape of her nose from Zira and the color from Tojo.

The "Zira is Scar's daughter/related to Scar in some way" idea is somewhat new to me, but interesting. It certainly does explain the similarities between the two. I've seen someone else theorize that they were half-siblings as well.

I actually came up with a crazy theory based on the "Ni is Kopa's real father" idea where Ni and Nala meet when Nala leaves to look for help and in the time they spend together, Kopa is conceived. Though Ni is unable to help Nala, he promises to come back to her homeland eventually. When he does, before finding Nala he learns out that she now has a mate and feels shocked and betrayed. However, he notices a cub with Nala that he realizes must be his son wandering around the Pridelands, and begins watching him from afar. One evening, he sees a pale lioness attack the cub and he fights her off, fleeing the land with his injured son. When Zira returns to the pride, Simba smells Kopa's blood on her, accuses her of murder and exiles her and Scar's followers, despite her protestations. I haven't worked out what happens with Ni and Kopa after that, but it's just what I've come up with so far.

I must admit that wereberus' antics inspired me to start toying with theories and drawing more fanart somewhat as well. I started toying with the idea of Ahadi being Mohatu's son and Uru being the selfish lion's daughter. For the first time I noticed how much darker than Mufasa Ahadi is in TLK6NA, and speculated that perhaps his mother could have been bright gold and Ahadi's coat was a mix between the colors of his parents, and if Uru were somewhat dark as well, Mufasa could have inherited his grandmother's colors while Scar would have gotten dark genes from both his mother and his grandfathers.

I also made a frightening discovery using werebereus' unique brand of "logic": According to him, Vitani must be Scar's daughter, since her undereye color is dark and Zira's isn't. However, both Simba and Nala have undereye areas that are slightly lighter than their muzzles and bellies, but Kiara's undereye colors are slightly darker than her muzzle and belly, so she couldn't have gotten that dark color from either Simba or Nala...and who is the only adult male lion with dark undereye fur that could have fathered Kiara? That's right: SCAR! :O