I want to know if my interspecific interbreeding is realistic or a total fiction.
Most animal hybrids are sterile (mostly the heterogametic sex according to Haldane's rule). Some famous examples include mules and ligers. Some famous exceptions include most hybrids from the Canis genus (dogs, wolves, and coyotes) and grolar bears.
In my world, there are sixteen living human species (mammals from the Homo genus): anatomically modern humans, merfolk, angels, demons, ogres, dwarfs, halflings, giants, vampires, therianthropes, goblins, trolls, orcs, elves, gnomes, and wizards. They can all interbreed with each other, but female human hybrids are more likely to suffer from endometriosis and PCOS, and male human hybrids are more likely to suffer from oligospermia and teratospermia. That said, most hybrids, both female and male, are still fertile (it is more correct to call them sub-fertile).
So, I wonder if the fertility problems are realistic, because my species have a radically different appearance (merfolk, ogres, and giants have a seal-like blubber, vampires have fangs, therianthropes are covered with a gorilla-like fur, angels have huge hands like a bat's wings, demons have horns, etc.).
They also have different behaviour (demons are eusocial, therianthropes are as solitary as bears, giants, ogres, and merfolk are as solitary as orangutans, etc.).
Naturally, they are of different size (merfolk are as massive as belugas, giants are as massive as polar bears, ogres are as tall as the average anatomically modern human NBA player and as heavy as adult male gorillas, angels are as big as wandering albatrosses, in a colony of demons, at a metric tonne, the queen is always the largest individual, gnomes are as small as domestic cats, orcs are as heavy as adult male American black bears, etc.).
Finally, they have a different diet (ogres, merfolk, trolls, halflings, and wizards are all obligate omnivores like brown rats, demons, vampires, therianthropes, dwarfs, and orcs are all omnivores with carnivorous tendencies like raccoons, angels, giants, elves, goblins, and gnomes are all omnivores with herbivorous tendencies like gorillas).
Note: since my story is a satire against racism and speciesism, my species can be of any morality (I hate both the Exclusively Evil and the Always Good tropes).
Note 2: when I say my story is a satire against racism, there have been persecution, wars, and slavery between anatomically modern humans and other humans, there have been some genocides, but many survivors, and some females apparently became sexual slaves. Naturally, anatomically modern humans considered themselves the "perfect human", and the discrimination mostly concerns other human species. But, fortunately, there have been some consensual marriages between all human species, sometimes, because some non-anatomically modern humans were considered "honorary anatomically modern humans", this is comparable to "honorary Whites" in Apartheid South Africa.