Apparently you need to be RH- to be abducted by aliens. Go figure, even aliens are discriminating.
+If a demon and an angel reproduce it's called a lie. Angels can't reproduce hence the lack of reproductive organs. Demons, in essence, are bad spirits/negative entities, basically spiritual abominations with no physical vessel, hence no reproducing can happen.
Yes, angels can take physical human forms. Can they reproduce in those forms? Yes, see statement before previous. Angels and humans offspring are called Nephilim.
Yes, demons can also become physical manifestations in the form of possession. Can they reproduce in those forms? Probably but they never do because they are too bent on destroying their victim than to think any further than their blinding hate. Plus they're probably a bit preoccupied fighting not only the soul of the person they are possessing, but also the priests and the angels appointed to all those involved in the exorcisms.
I'm just saying. There's no way a demon can reproduce with angels or humans or other demons, nor can I see any of the others wanting to.
++I've got to go change a dirty nappy, and do the dishes. MEEEEEEEHHHHHHHH.