Given the rather cosmopolitan atmosphere in the three city-states of Eorzia it seems pretty common for their to be cross-specie romances. Whether these unions produce children or not is unknown as far as I know but the morphology of the species seems pretty similar to a human/hyur that the mechanics of sex and child birth are probably pretty similar across the various species that make up the city-state populations, excluding the occasional beastman.

There does not seem to be any stigma to such unions or dalliances so we can assume that these kinds of relationships have been happening for some time now and says much about the rather open nature of Eorzia society. It's a melting pot.