Well, I would not go fishing for trouble with researching this, but I have to share some things.
First off, there was a famous movie called Rosemarie's baby some of you are familiar with
A new wife was tricked into having sex with satan during an occult ceremony
The child was suppose to become the anti christ I believe.
This happened in the 60's, about the time that the real AC may have been born
The woman who played the part of the new mother was Sharon Tate.
Sometime after the movie she was murdered by the crazy demonically possessed Charles Manson group.
The Director who was married to this actress was involved in a scandal of having sex with a 14 year old I believe.
He fled to Europe and they have protected him from returning to the states for trial ever since.
 
Now, as far as demons having sex with humans and producing offspring.
Well, when did demons ever follow rules?
I know of a couple instances where people have told me they had sex with demons.
This was not in their sleep, but while they were awake.
But can they produce offspring?.
I don't know, but I suspect it is possible.
There are, it seems, some born for hell.
But, I would like to say that the bible does not indicate that Eve had sex with the serpent.
Careful with this UFO stuff guys.