I wanted to chime in because I can see pushback to OP's theory. For me, this is not the first time I have seen the theory that Cain is the literal son of Satan. I first heard about this a few years ago when I stumbled upon a video from Dr. Gene Kim (Pastor with Youtube channel Real Bible Believers). Dr. Kim backs his teachings with bible passages.

I remember things finally starting to click in my head and make sense after watching that video, especially when it comes to bloodlines.

Although I cannot find that video right now. I did find a similar video that expounded on that original teaching titled "VERY WEIRD! What Really Happened to Satan & Eve?" https://www.youtube.com/watch?v=bA0PN8gz2k0

To me, it is clear that Eve spent time with Satan because he beguiled her and was able to trick her. Based on that, I believe that Eve laid with Satan and became pregnant with Cain, & that she also laid with Adam and became pregnant with Abel.

There are bible passages to back up that theory. Most notable are...

1 John 3:12 from Geneva Bible:

12 Not as Cain which was of that wicked one, and slew his brother: and wherefore slew he him? because his own works were evil, and his brother’s good.

Matthew 13:36-39:

36 Then sent Jesus the multitude away, and went into the house. And his disciples came unto him, saying, Declare unto us the parable of the tares of that field.

37 Then answered he, and said to them, He that soweth the good seed, is the son of man,

38 And the field is the world, and the good seed are the children of the kingdom, and the tares are the children of that wicked one.

39 And the enemy that soweth them, is the devil, and the harvest is the end of the world, and the reapers be the Angels.