I have a little different angle
I thought I would share what I believe, maybe you can use some idea from it:
The scriptures say that God created man a little lower than the angels, so He did create other beings. And, those angels are able to interact with our physical world and according to scripture, do so. But their place of residence is considered the heavens. The scriptures also reference a war in the heavens that is going on, even as we speak. That spiritual warfare involves physical man as well as spiritual beings. According to scripture, when Lucifer was kicked out of heaven and given dominion over the earth and the power of the air, temporarily (which is still in affect), one third of the angels followed him, leaving their heavenly abode in rebellion to God. So, the scenario at this point, according to scripture is that there is humanity, angels, demons and satan as created beings.
Here's my take on the whole thing: According to scripture, man/woman is created in the image of God, nobody else. And, God being the creator has bestowed on man/woman the gift of being able to procreate which is a God act (to create). No other beings are able to do this. I have read many reports of how aliens supposedly kidnapped human beings and then performed experimentation/examinations on them that seemed to focus on the reproductive system. There have also been reports from abductees that they saw what looked to be human children on board some of these spacecraft. Also, there have been reports that women that were abducted while they were pregnant, unexplicably returned home no longer pregnant with no explanation as to what happened. I think the movie "Communion" with Billy Crystal is a very good example of what I'm talking about. That movie was supposedly a true account.
I said all that to say, I believe that the reason aliens would possibly be focused on humanity's ability to procreate is because the aliens can not and desire to be able to reproduce themselves. If they are beings and can cross between dimensions of existence, and they are fallen angels, created by but in rebellion to God, and there is only a finite number of them, I think they are trying to increase their numbers by trying to devise a way to reporduce themselves. I also they are jealous of our ability to procreate. Since, satan's bent is to mock God, it follows that his minions would have the same drive. Also, since satan is under the self-perpetrated delusion that he is going to usurp God's authority, I would think satan et al would be deranged enough to believe that sheer numbers will overwhelm God and so become obsessed with trying to propogate themselves.
I don't know if you can use any of that but thought I would share.
kdnxdr
ps: I think it's important to not that there are different concepts as to what "the heavens" are. This is not just a reference to somewhere "out in space", it has in interesting dimentionality to it.