Mheetu would be cannon but deleted cannon since his character was a concept deleted before the film was made and only made it into early planning stages. We really have no idea of his official color (probably pale, but again we only have sketches). There is no official information about his character.
In the Lion Guard, it specifically states Kiara is going to be queen of the Pridelands, thus making her the eldest. It does kind of make the timeline wonky, but so does SP
So the only official cannon cubs of Simba and Nala are Kiara and Kion.The whole reason for the confusion before SP was the the creators of TLK did not plan a sequel or think TLK would become so HUGE a success. I think the cub named only "Fluffy" (officially) made most fans think it was a male because the cub resembled Simba as a young cub. Before SP was released, TLK6NA was made and other books listed the cub as the son of Simba and Nala. One of the biggest and most revered fanfictions still is Chronicles of the Pridelands which made the cub a male. However, after SP this was cleared up as the cub is referred to as Kiara.
