Well, there's no doubt about high risk of getting issues. I hope those sons just somehow can survive through years they live with their crazy mother, but somehow I doubt so. After all, their father used to beat them. What else there was left for them than their own momma? No one. And under such conditions mother's power and influence is huge.
I don't know about other two (are they just acting for their mother or are they already be twisted by their mother) but I say "Brandon" is rebelling against his mother and her views. There's nothing weird in teenagers watching porn, but doind so everytime when he gets the chance is mark of rebellion, not ****ed up mind.
That's what I believe anyway