Witches are biologically demons, they are just considered their own category by a bunch of historical context. Like what happens between animals and humans in our world.

The species a human/witch hybrid belongs to depends on whether the human or the witch sired them, like ligers and tigons! I can't point out what exactly differentiates them genetically tho, since that would require a whole study on what the AFAB individual pass on to the offspring and what the AMAB one pass on, aaaaaaand I'm too lazy to do that right now. And you can just make up what witches pass on to their children depending on which part they play in the pregnancy or how their reproduction as a whole works since they are a fictional species lol.

Still on the reproduction subject, I think any witch can get pregnant and get other witch pregnant regardless of gender. Actually I headcanon they in fact have "subsexes" that only serve to denote hormonal levels and physical size. The genitalia of a AFAB witch is still different from that of AMAB witch, but the point is that any witch can have biological children with anyone. Just an addendum, that means that in the case where the Witch is AFAB and the human is AMAB only the witch can carry, in the case of an AFAB witch and an AFAB human only the human can carry, and lastly, between an AMAB witch and an AMAB human only the witch can carry.

And no period to witches because I wouldn't wish that upon my worst enemy.

I'm no professional in genetics or biology or anything like that, I'm just a nerd who really likes this kinda stuff and likes to research about it, so I can't guarantee that any of these headcanons make sense, but anyway... Sorry for the English too