I actually think that they may have been having some problems and that was one of the reasons that Shan'ann visited so long in NC. She was thinking that absence would make the heart grow fonder. In Chris' case it was out of sight, out of mind.
I do think that he liked the bachelor life; however, it would have come at a high price. He wasn't willing to pay that price. In his psychopathic mind, he figured that murder was the answer.
I agree that normal parents have a deep love for their children. There is no way that a normal person would even think of murdering his/her children. The instinct is to protect. In Chris' case, he was so self-centered and self-focused that he didn't have those feelings.
I also believe the constant conflict surrounding Shan'ann and the girls gave him an extra incentive. If you notice, his parents asked for Chris' things back from the house and asked for nothing of their grandchildren. That, to me, shows that they also had little to no attachment to his girls.
I hope you all realize that I am just speculating and can certainly be wrong. I often am...My husband would certainly agree with that sentiment.