From things they've said I think, such as what Rebecca said about what his "real parents did to him", I think Chris knows all the info on Kristen and Jeff. What they did to him sounds like Jeff selling him, just giving him up for adoption wouldn't have that sitng.
For what it's worth, what did Kristen do to Christoper. She didn't sell him or abandon him. She just took drugs and died.
I always thought it seemed out of character for Kristen to develop a drug problem, she seemed too in control for that. I do think that JR probably pushed her off the balcony while arguing with her, but he probably meant just to push her away from him when she got in his face and she went over the balcony unintentionally.
Chris having regular secret contact with Pam would be an amazing shocking twist. I had never thought of that.