would a shifter and an orc be capable of having a child? Not usually. The fact that humans and orcs can reliably produce viable offspring was a surprise and is the foundation of the clan culture of the Shadow Marches; half-orcs are celebrated as proof of the bond between the two. Other matches aren’t impossible, but definitely rare.
— Keith Baker (@HellcowKeith) April 27, 2020
What about humans and shifters? AFAIK it hasn't been defined in canon, so it's ultimately up to the DM. PERSONALLY I'd say "Not reliably." They're different species. We've called out that elves and humans were astonished when the first half-elves were born, because they didn't think reproduction was possible.
— Keith Baker (@HellcowKeith) April 27, 2020
We've called out that *changelings* can reproduce with anyone, and that Kalashtar are effectively human for purposes of reproduction. Otherwise I'm inclined to say that successful hybrids are rare. But House Vadalis, manifest zones, etc could make anything possible.
— Keith Baker (@HellcowKeith) April 27, 2020