I've thought about this theory before, what if they're all only related to Zira? There are 'semi canon lions' that could somehow exist in TLK that could of sired them and not be related to Scar at all.
- You know, there IS a resemblance between Nuka and King Joe.. Maybe Zira's genes, passed down from her father could be why he LOOKS like Scar.. but he's really the product of Joe and Zira?
- Tojo has Vitani's 'blue' eyes and pink nose, but Zira's genes are what give her those 'sharp furry cheeks' and 'bushy eyebrows'. OH and Tojo gives Vitani her ear-rims!
- Chumvi and Kovu have 'brown fur' and the 'head tuft', But Zira could give him the 'furry cheeks' and 'outsider nose' oh and perhaps his 'green eyes' are from his grandmother?
It's a stretch but it just came to me! what do you think?