I literally thought that he was going to treat his son better because he was their son but...

Like legit most yandere characters are like "it's a clone of the thing I love" or "it's a piece of x person's body" or "it's a product of our love"

EXACTLY!!

I will admit though it's rare to see a yandere only want the purest form of their desires not diluted by their own blood but that would require some actual character exploration on self worth and valueing of the self and I don't tje writer wants that.