I want to write a science fantasy novel about humans evolving into five new species. The five races are: the Groses and Grosettes (they are my Ogres) (their name comes from the french word gros/grosse that means fat, big, large, overweight or obese) (I am a francophone from Quebec), the Dwarves, the Giants and Giantesses, the Skeletons (they are my Elves) and the Mundanes (they are the "standard" humans).
The Mundanes live everywhere, the Dwarves live beneath the ground like moles, the Skeletons are arboreal like spider-monkeys, the Giants and Giantesses live in freshwater like goldfish, and the Groses and Grosettes live in saltwater like whales.
The Groses and Grosettes have evolved from Austronesians (Polynesians, Micronesians, Filipinos, Indonesians, Malaysians, aboriginal people from Taiwan and aboriginal people from Madagascar). The Skeletons evolved from aboriginal people of South America. The Giants and Giantesses evolved from Central Asian and South Asian people. The Dwarves evolved from Europeans. The Mundanes come from all origins.
I want my Groses and Grosettes to be obligate carnivores like penguins (their favourite food is decapods) (decapods are lobsters, crabs and shrimps). I want my Dwarves to be facultative carnivores like dogs (their favourite food is insects) (insects are flies, moths, ants, bees and termites). I want my Giants and Giantesses to be facultative herbivores like oxen (their favourite food is plants of the Malvales order) (Malvales are cocoa, durians and mallows). I want my Skeletons to be obligate herbivores like sloth (their favourite food is plants of the Rosales order) (Rosales are apples, pears, roses, strawberries, cherries, almonds, elms and hemp). I want my Mundanes to be true omnivores.
I heard somewhere that humans cannot be obligate carnivores because of the lack of vitamin C synthesis. But I know four types of obligate carnivores that need to consume vitamin C: pikes, salmonids, swallows and tarsiers. I think a species that lack vitamin C synthesis could be an obligate herbivore if it eats fruits and not only seeds.
So, is it realistic for humans to evolve into such creatures?